Hey Lindy74. Nice progress. I'm a couple months behind you on a very similar bid so it's cool to see how your doing it. What size tubing did you use, especially for the cab over section? looks like 1 x 4" ?
I've been searching out what to use for the siding, and all of the filon I can find is heavier and more expensive, so I am going to go with smooth, pre-painted trailer siding (white for me) that comes in a variety of sizes. It's .030 thickness. I've heard advice to go thicker or even thiner, but this thickness gets used on a bunch of enclosed trailer around here and seems to work. Also I think some airstreams are only slightly thicker. Here is one supplier, but there is a variety out there online.
http://www.mirageinc.com/030-beveled-aluminum-full-skin-sheets The roof i'm going to use a rolled aluminium slightly thicker - more like .040.
I've been wondering about the curved roof too. It's definitely going to be stronger that way, but it means a complexity added to the project that I'm not sure I want to deal with. My current wood framed camper, and my buddies all have flat roofs, so it seems pretty reasonable to have one as well. The roof i'm going to use a rolled aluminium slightly thicker - more like .040.