I started the build this many moths ago. It was the winter of 2008, it was a cold winter here in Utah so work ont he trailer was slow and cost a lot of propane to heat the shop. Here are some new pictures and some new found information.
This is my Steel chop saw. Or cut off saw, It is a Milwaukee. I have been impressed with it, with on exception the switch broke on me so now I use a plug strip with a switch on it. This plug switch also has a circuit breaker on it which has come in handy. I am cutting the base pieces using the 45 degree angle idea. I plan to put the base together so it is air and water tight. This will help with river crossing, as well as rust issues. Welding the 45 degree angles is pretty easy. I will weld them really well and grind them clean so the welds will disappear.
Here is a quick garage sketch of the base sizes. I had to revise my plan and I made the base 50 inches long so I can have a 48 inch length inside to fit my nice piece of 4 x 8 Aluminum diamond plate. The base will be exactly 48 inches on the inside from front to back. This way the two side and the bottom will fit from the 48 x 96 inch piece really well.
This is the top view of the Trailer plans. I am making a few changes to make sure the box fits what I want.
This is the base as it was taking shape. When building a box, be sure to check it for square on each corner using a big steel square and then measure the diagonal both ways. If the diagonal measurement is the same then the box is square. I made the outer box then I cut the two cross pieces to the exact length. I could have cut every thing at once but as it turned out the box is about 1/8 of an inch wider than the 40 inches I planned. So the cross pieces are a bit longer than 40 inches as planned.
At this point I have the base done and I started working on the sides. This is where I made a serious design change. The top is still made out of 2x2 square tube .060 wall thickness. But my original plans called for side that are 26 inched tall, with a nice 24 inch inside height. So let me explain the change I made and how I got to the decision. I built the box to look like it is in this picture. The the other guys in the shop at the time. said "WOW that is tall, are you sure you want the sides that tall?" This simple little comment cost me about 2 hours. I looked at the box, I agreed, it was really tall. Then I got back on the Internet. I did a search for off road jeeping trailers and looked at as many pictures as I could find. The overall conclusion I came to, was the trailer needs to be the same height as the tub on your tow rig. In my case I am towing it with a Jeep Wrangler TJ, which has a rear tub that is 19 inches tall. When the tow rig and the tow trailer are the same then they look good and match. When I thought about how high the trailer was going to sit and how tall the sides were that I had planned 26 inches was way too tall. I got out the grinders and took the tall sides off and cut them down to 17 inches. This will give the trailer sides a total height of 19 inches to match my TJ. I rebuild the sides and now I am very happy with the end results. I also decided not to put any pieces down the side of the trailer. I was planning on two 2x2 square pieces at the same places as the bottom inside bars. I am leaving the side open because the box is really strong as it is and once I get the tires and axle on I will see how they fit, and how my fenders may fit. At this point I may use some smaller angle iron to support the side walls. So this is one more design change on the fly. I did end up with one side bar right in the middle made out of 2x2 square tube in .060 wall thickness.