Used or new?
Biggest thing to remember about these things is they are rolling earthquakes. There is always something needing fixed on them. Doesn’t help some of the parts used are the cheapest pos parts I’ve ever seen and those are the “good ones”.
Tires/bearings/brakes are usually my #1 check. If your rolling on 3-4 years are “eh” as far as if the tire is still good. Depends on your location and how it was stored. Older than that and your asking for a blow out. Don’t use the grease zerk at the end of the spindle, it will blow grease into the brake drum (if it has bearing buddies, different deal). Make sure brake magnet, shoes and drum is free of grease.
Depending on age and mileage, spring shackles and bolts should be checked. They ride metal on metal (no getting around it) and eventually start to oblong the hole in the shackles or cut through the bolts. Cheap and easy to fix those.
Any delamination on the outside of a fiberglass sided rig (mainly front corners do this) is NOT from heat. It’s almost always water damage from the roof leaking around the edges. Walk ALL the floor around the edges for real soft spots, again, water damage from leaks. Number one damage issue is water damage in these things from improper care of the roof or anything attached to the side that was not sealed to the body. Get up on the roof and look for any cracks or tears. Even just cracks in the sealer is bad.
The older they are, the more work they require. Sun is killer on plastic parts.
If it has a genny, start it and let it run for a while while you walk around it. Then turn the a/c on and the microwave on and see if it surges. Means carb needs cleaning or replacement.
Propane tank age also, after 12 years they need recertification.
Larger the water tank, the better. Specially for first time camping moms and kids. Lay down the rules on just enough water to get wet, off, rinse, off lol. Even with 160 gal of water in my trailer, we can burn through that at the dunes in 6 days