I started my build yesterday! Scratch built frame is almost done. I used 2x2x.125 and a 3x3x.125 tongue. I've never welded before, but a friend who has gave me a quick tutorial and away I went. Flux core MIG is easy enough for beginners. It aint the prettiest welding you'll see but it works. It's the grinding and clean up that take the most time.
I ordered my steel 60" across but later realized I needed to deduct 1.5" for wall thickness. I ran back to the steel shop and asked for that amount taken off and when the yard monkey came back with it it was cut to 57.75"
But I figure that will not be an issue in the end. the bed will be 58.5" as required and I can add a filler strip of wood between the bottom of the wall and the frame if need be.
As per your advice on my original question, the tongue will be 5' long. Axle and wheels are next on the list.
This is gonna be fun!!
99% of the way done with a Generic Benroy. Only because these might never be done if you like to tinker. But it's on the road!