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Fiberglass M416/M100 Military-style Trailer Tub Kit
02-05-2013, 01:19 PM
Post: #1
Fiberglass M416/M100 Military-style Trailer Tub Kit
I've been working on a new fiberglass trailer kit idea, this one is patterned after the military M100/M416 trailers. The military-style trailers are very popular among the adventuring, overlanding and off-road crowd, but reasonably restorable original military examples are getting very hard to find, and the new versions of these trailers offered by trailer vendors are very expensive. So I've designed and will be building a fiberglass military-style tub kit that's intended to be very affordable and assembled in a home garage or driveway by a DIY-er.

I've built a set of 1/4 scale molds to test the design and assembly concept of the trailer, here are a few photos of two 1/4 scale trailers I have built using tubs that came out of these molds. On the left is a 6' tub (same as the original military trailers), and on the right is a 4' version.

[Image: MiniM416s2.jpg]

Here's a more "optioned" view of the 6' tub (I'm calling the 6' version the M-72 Smile).

[Image: FenderTable.jpg]

Both of these models are sitting on scale models of Harbor Freight trailer frames. The 4' version frame has the original 12" wheel/21" tires that come with the frame, and the M72 is sitting on scale replicas of 31" tires on Jeep Moab alloy wheels, which share the 5-on-4.5 bolt pattern of the larger HF frame. Here's the model 4' tub sitting next to the model Harbor Freight Mini Trailer frame:

[Image: FendersMini.jpg]

The 6' tub can also be bolted to an original M100 or M416 military frame to replace a rusted or beyond-restoration original military tub.

In this thread I plan to post lots of details of the design and construction of the full size fiberglass molds and my first full size prototype trailer out of those molds, and I'd really appreciate as much constructive feedback from you as possible. I'll also try to give plenty of information on the techniques I'm using, for example fiberglass and mold making, so if you're interested in learning stuff like that the thread should help you. If there are features or capabilities you think I should add to the design, please post them.
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02-05-2013, 03:41 PM
Post: #2
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
I'm watching this thread!!! Cool stuff indeed.

""Specialization is for insects."
Robert Heinlein
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02-05-2013, 03:45 PM
Post: #3
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
Awesome Jeff. Looking forward to it...

Check out my trailer build: SawTooth XL Off Road Trailer
Visit my site: http://www.sawtoothent.com
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02-05-2013, 05:25 PM
Post: #4
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
BTW if anyone is wondering how large a 1/4 scale military trailer is, here I am experimenting with jerry can placement...

[Image: ModelCans3.jpg]

It'll be nice to work on the 1:1 scale version now after doing these little ones Smile.
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02-05-2013, 07:00 PM
Post: #5
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
Love the detail in the models, although the rims aren't up to you'll usually quality level Smile

Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping
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02-05-2013, 07:17 PM
Post: #6
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
(02-05-2013 07:00 PM)Scott Wrote:  Love the detail in the models, although the rims aren't up to you'll usually quality level Smile

Hey, these are concept models, not contest models Smile. If fully detailed wheels would have meant that my design for the full scale trailer could have been improved, I would have done something more than just use printouts for the wheels.... but I did go to the trouble of photographing one of the wheels on my Retro Wrangler pickup and printing it in 1/4 scale... then I glued the printouts to the scale tires I made from MDF and turned on my drill press to add grooves to simulate the tread. I definitely spent too much time on the model wheels and tires!
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02-06-2013, 05:27 AM
Post: #7
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
These are the main requirements that guided my design process:

1. Very affordable. The parts for the tub kit must be cost-efficient to manufacture so the kit can be offered at a very affordable price.

2. Military trailer styling. The goal isn't to create a 100% "rivet counter" correct trailer tub kit in fiberglass, the goal is to create a reasonable replica with appropriate modifications to make it easy and cost-effective to manufacture and ship, and affordable and strightforward for the DIY-er to build.

3. Frame choice. The tub kit must be installable on an original military trailer frame for those who need to replace a rusted-out or damaged M100 or M416 trailer tub, but it also must be installable on inexpensive Harbor Freight trailer frames, or custom-built welded trailer frames.

4. Modular. The tub kit must be modular so that different versions and options can be offered and built; modularity should also allow the unassembled kit to be shipped UPS Ground instead of Truck Freight to keep costs down.

5. Tailgate. Unlike the original military trailers, which don't have tailgates, this tub kit must support the installation of a tailgate.

If anyone has any additional requirements they think this kit should meet, let me know.

All of the above sound like I'm designing a commercial product so I should explain something... although I'm just a hobbyist who designs and builds these things for fun, I always design things so they could be commercial products - a number of my designs have been picked up by companies and are now on the market.
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02-06-2013, 10:35 AM
Post: #8
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
Based on the requirements I listed, here are the main design features of the tub kit:

[Image: DesignFeatures1_zps03f44417.jpg]

- Modular assembly. The kit will consist of two end panels and two side panels. There will be both "solid" end panels and "tailgate" end panels. A tub can be assembled with one of each end panel type, or two solid ends (like the original military trailers) or with two tailgate ends.

- Tailgate. Cutting a tailgate opening into an original military trailer greatly reduces the structural integrity of the tub. This tub kit is designed to be strong with a tailgate opening. The tailgate opening is the same size as the Jeep CJ, YJ and TJ tailgates, so there are lots of options. The Dinoot smooth fiberglass tailgate will fit for those who don't want a Jeep-styled tailgate.

- Multiple versions. Also because the modular design, several different length versions of the tub can be molded, up to 6' long. I envision a 4' long version to install on the very affordable Harbor Freight Mini Trailer frame for people on a very tight budget or for people who just don't need the space a 6' trailer provides. There are photos of a 4' concept model in first post in this thread. For the time being I'm calling the 6' version the M-72 and the 4' version the M-48.

- Frame. The tub can be installed on an original M416 or M100 frame to replace a rusted or damaged original, or it can be installed on any frame of the user's choice, including a budget-friendly Harbor Freight frame.

- Fenders. I've also designed sheet metal replacement fenders for the original M416's and for this kit. They could cost-effectively be manufactured in both 9.75" wide (same as the original M416), or in 12.75" width to cover wider tires, in the case where someone wants to run the same tires/wheels on the trailer as he does on his tow vehicle.
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02-07-2013, 05:24 AM
Post: #9
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
As I posted earlier, the basic tub design consists of 4 fiberglass panels - 2 ends and 2 sides, bolted or bonded together at the corners - here's a concept drawing of the 4' version of the tub on a Harbor Freight frame:

[Image: M48Assembly2_zps20be259e.jpg]

The overall dimensions are very similar to the original military trailers, this drawing shows the 6' version, although the only difference between the 6' and the 4' versions is the length.

[Image: M72Dimensions-1.jpg]

Length - The molds and side panels are designed so that tubs of any length up to 72" can be made. The 72" length is the same as the original military trailers; a 48" length is perfect for putting on a Harbor Freight Mini Trailer Frame, which can regularly be bought for $175.99 on sale and with a coupon.

Top width - The top width (outside dimension) is 47.5", vs. 48" for the original M100 and about 51" for the original M416. This dimension is slightly smaller to make it easier to DIY-build a hard cover for the tub out of a 48" wide sheet of plywood.

Bottom width - The bottom outside width is 40 13/16". This dimension is a good fit on the frame width of the HF Mini Trailer, and also matches the frame width of the original M416's. This width allows clearance for most "tow-vehicle-sized" tires on the Harbor Freight 5-lug axles without needing a wider axle or wheel spacers (more on wheel sizes/offsets/tire sizes later in this thread).

Height - I've designed the tub about 2" taller than the original M416, this is mostly to allow vertical space below the tailgate opening to be able to bolt on stock Jeep CJ tailgate hinges. At the original M416 height, the vertical area below the tailgate would only be 1.5" high, which isn't enough height for CJ hinges.

Tailgate Opening - The original M416 trailers don't have tailgates; one of the reasons for this is so the M416 can be watertight and float. You could build one of these fiberglass kits that way with two solid end panels, but I'm guessing most people will want a tailgate. The tailgate opening will accept any factory or aftermarket CJ-7/CJ-8, YJ Wrangler or TJ Wrangler tailgates, or the Dinoot smooth fiberglass tailgates can be used if someone doesn't want a "Jeep look" on their trailer.

I'm starting to work on the mold masters now, so I'm committing to these dimensions. If anyone's got any comments on the dimensions speak now or forever hold your peace Smile.
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02-07-2013, 08:52 AM
Post: #10
RE: Fiberglass M416/M100 Military-style Trailer Tub Kit
Overall looks great. Like the revised top dimension for using 4' plywood for a DIY cover. I'm wondering about the bottom width. The dimension I'm wondering about is the bottom width for being able to accommodate both the HF 40x48 and original 41" wide frames. On a 41" wide frames there will be almost a 1/4" step between the frame and tub sides that will effect fender attaching. My experience with HF frames is the tire to frame clearance in normally pretty tight. Reducing the clearance by a 1/4" with stock tires could be a problem. What I didn't know is if the 40x48 frame is a true 40" wide.

Scott Chaney - Owner of Compact Camping Concepts
Home of the DIY Explorer Box and Dinoot trailers, also Tent Topped camping
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