1) Look where the top meets the front and rear panels on the inside for stained wood which screams WATER INTRUSION and probably some degree of rotten wood framing.
2) Same thing around the roof vents...staining says it has been leaking
3) Check around the window frames for staining/damage to the interior from water indicating some possible rotted wood.
4) Look at the bottom section for stains/leaks where eyebolts have been attached
5) Look at the front/rear panels where they meet the side panels to see if the aluminum trim has been distorted or is loose and if the wood in there is "soft" when you poke an awl in there if it is open
6) Look at the bottom of the camper for soft wood or loose, rotted wood.....hard to do without being able to see it up on jacks or a rolling frame off of the truck
7) Follow the plumbing system to see if anything has leaked/seeped and rotted anything. That means from the fresh tank to sink to discharge outlet
8) Try to check the electrical system. Maybe that means an extension cord and some 60-watt light bulbs or someone who understands solar/batteries/inverters (like Vic!). If it does not check out, keep looking!
Alaskans and other "old" (40 years old?) campers that have no paint left on the exterior and exhibit a lot of wear on the interior may be OK but if you are patient and are willing to pay a bit more, you may find one that was not beat to death and was parked in a garage or a barn to keep the sun from eating the paint and the seals. Conversely, if you are OK with buying more or less a "pig in a poke" and are ready to perform major surgery (carpentry) then you may be OK to take on a "project" camper.
The one in the LA CL for $2400 has been there for a few years. I see it as a major project and as such is probably more like an $800 item personally….and I was not interested in one like that....even at $800!