Batteries $100/each. Tires $100/each (spare too). 7 years old? JUNK. Brakes. Stains on interior walls or ceilings. Walk on roof. Walk on every square inch of floor you can. Any soft spots? Hook hose to inlet. Pressure check every water line you can. Fill each holding tank. Look for leaks. Run the water pump. Turn on every appliance...stove, oven, AC, heater, water heater, smoke detector, lp detector, shower, toilet, sinks. Exterior siding delamination (bubbled siding). Check the date on the propane tanks. If they are 8 years old or older, they need to be replaced or re-certified (was 12 years). If tires are over 7 years old, they are junk.
Now, if you have a friend that's into RV's....drag him along (two heads are better than one). If you find a trailer like my 20 year old 5th wheel ($3,500), you would skip paying $15,000 for one. They are out there.