Welcome to the forum, and welcome to the world of RVing. Lynda and i have put together a list of things we would check. You may already have these things on your list, but here are some of ours. They are not in priority order.
We would try to find a knowledgable RV technician, someone we trusted, to go through the entire coach. Maybe someone on this forum in the Phoenix area could recommend someone.
We would also want to see all manintenance records the owenr has on the coach. We would look for oil filter change intervals, transmission fluid change intervals, and repairs for leaks, etc.
Check the DOT date on the tires. You don't want to have to replace them, but if they are older than say 7 years, you should probably replace them for safety. They will be an expensive item.
If the coach has been sitting a long time, oil seals can harden and crack producing leaks. Check all seal locations including the front wheel bearings, etc. Assuming you purchase the coach, we would then change the fluids and filters to give you a fresh start.
Check the roof to be sure it is OK, and the seals don't show cracking. Also check the sides for "bubbles" which would indicate delamination. If we saw delamination, we would walk away from the coach.
Make sure all the accessories, water heater, water pump, microwave, generator, refrigerator, tvs, furnace, etc. work properly. If it has a convection oven, make sure the metal shelf is with the coach.
I'm sure others wioll add to the list, but that's what we would do. Good luck.
Jim and Lynda, (Sophie, Jake, attack trained killer Shi-Tzus :-))
2003 Fleetwood Expedition 38N 2005 Saturn Vue