My buddy wants to make a toter home that will carry a race car. he wants to build a 2 level unit for 2 cars. He built a motorhome conversion some years ago, but needs info on building the second level

Seems like a good idea? Anyone ever seen plans offered? The converters probably have an engineer/draftsman or something along those lines to work this stuff out. Could just find someones you like and ask to take a lot of pictures and see if you can improve on it. I would like to see a list of materials on what to use where. 2x2 box steel where? How thick.. .12 or .08 or ? That sort of thing. Probably a great deal could be copied over from the coach conversion folks.