Thanks Oleg and RationalEx!
The supports seem much more solid, thankfully. As for weather proofing, first I'm going to install some kind of drip edge that will be attached to the folding walls and will cover the gap when the walls are up. Then I'm going to put in some weather stripping, but that will be tricky because the gaps vary. It's not going to be completely airtight anyhow because I need ventilation and will be putting in some vents.
My recommendation for anyone looking to do something similar (folding, slanted shed roof) would be to do something along the following lines:
1. Reduce the height slightly (mine has about 6'8" at the tall end and 5'8" at the low end) - maybe 6' or a touch higher at the tall end.
2. Increase the height of the base walls somewhat to reduce the weight of the folding components.
3. Consider making it a clamshell with the roof hinged directly to the base in the front or the back. I think this would make setup/teardown more accessible for more types of people. I'm not a big or particularly strong guy, but I am an able-bodied, active sort, and even with the gas struts there is a moment (when the side walls are folded down and I'm folding down the back wall with the front wall still up) when I'm sort of guiding the whole roof down, surfing the power assist of the struts as it were. I think that moment could be tough & potentially sketchy for a lot of people older, slighter, or with less upper body strength. Once the back wall is down and the roof is resting on a fulcrum at the back, the front wall comes down without that "surfing" moment.The clamshell design would eliminate the need to surf the roof down like that because it would always have that solid fulcrum.
I put the top door on today. Still need to install hardware, a strip of wood to cover the gap between the two doors, and a sliding barrel bolt or two to connect the two doors so they function as one when the camper is up.