I think there's a walkthrough on here somewhere so maybe someone can point you to it.
Check the roof, tires, sides for delamination, inside cabinets for any signs of leaks, soft floors,and all appliances. If it smell moldy then there is or has been a leak somewhere. Make sure any slides work and crawl underneath just to make sure there's no frame damage or anything out of the ordinary. Check the pin box for cracked welds. Just because tires have good tread don't mean that they're good tires. They can be old and still look good.
I'm sure some others will pitch in with their thoughts.
