Good news on the frame I guess, hopefully the wheel/axel/spring assembly is in good shape
The holding tanks should also probably be replaced. So you will be replacing the siding and putting on a new roof...there's a good used RV right there
Not to discourage but my guess is you'll be spending approx. 15 grand when all said and done two years from now
Now there's a nice used glamper with a slide out or two and you could be glamping next weekend 
Now there's a fun thing to do in your spare time...camping with the boys in a tent and cooking on a fire out in nature with no phones instead of trying to rebuild a 50 year old glamper
I could suggest many other things like fishing, sports, TV...to do in your spare time instead of working every spare minute learning by making mistakes...again, each to their own. You seem determined and I do wish you the best. So what are you doing with the new floor joists...may I suggest 2x8's at least and maybe pressure treated somehow fastened the old solid metal frame...maybe lighter I-joists is the way to go and 5/8" minimum T&G plywood...then the walls with your already purchased 2x2's...I hope they're strapped together to keep then straight, then install two rows of blocking/gurts to help keep them straight. The new walkable roof could be 2x6's 12" on centre cut with a nice curve and 1/2" plywood. I'm assuming you have a table and mitre saw in your arsenal along with a good jigsaw
I would also suggest that before you do anything you should have the frame blocked/jacked/supported 100% level back to front and side to side to make the building process somewhat easier
Again, good luck and keep the photos coming so I can critic 
Now there's a fun thing to do in your spare time...camping with the boys in a tent and cooking on a fire out in nature with no phones instead of trying to rebuild a 50 year old glamper
