These are great suggestions, thanks! Updated my location in the signature. I'm in the East Bay of San Francisco.
I found the owners manual online and printed it out, now going through it.
I woke up at 3am and remembered that the seller needs to have a smog check done (CA law) and that I can also order a carfax, though I don't know how useful that will be.
The truck/van piece I am comfortable with, planning on fluid changes, anticipating things like ball joints, shocks, etc. That stuff I am very comfortable with.
The radio doesn't work - seller said it might be a fuse. I plan on upgrading to a Carplay system anyway so no big deal.
The price is kind of set - seller agreed to let me have it checked out as long as it can happen quickly, and he's still showing the camper today just to have backup offers. Price is $12,500 which I think is reasonable (it's hard to find comps on this model).