I framed and sheathed each wall individually and then stood them up with the help of long 2x4 braces. My neighbor let me borrow his framing nailer, which made things go much faster. I added a second cap of 2x4 on the top to make the walls a little more rigid. I then laminated 4 2x4's to construct a ridgeboard. I nailed in some temporary 2x4 supports and had a friend help lift it into final position. Once all of the rafters are cut and nailed into place, the supports were removed.
The refrigeration setup in your van is an area where you really do get what you pay for, whether you’re paying in money or in time. The best options are the most expensive. The cheapest options are a pain and/or don’t work very well. And if you try to save money with a DIY refrigerator setup, you could end up spending a lot of time on installation.