Just a couple of thoughts:
Is it gasoline or diesel? If gas, the fuel tank must be removed and cleaned, and the carburetor on the generator will also need cleaned. If diesel, the fuel won't "rot" like gas does, so unless there is water in the tank it is probably OK.
There is no re-certification requirement for the frame mounted propane tanks on motor homes. Inspect the tank for damage and severe corrosion. If none or very minor is found, it is likely good to use. I would have a system pressure test done to verify that the regulator is still in good condition and working properly.
Definitely look for evidence of rodent infestation. Don't just look in drawers, pull them all the way out and look behind and under them. remove everything from under the bed and in the cupboards and storage compartments, clean and inspect everywhere. If droppings are found DO NOT vacuum them up! Use liquid disinfectant cleaners and carefully wipe them up. Surgical gloves and a mask might not be necessary while doing this cleaning, but they wouldn't hurt, and they are inexpensive. Rodent droppings can carry some rather nasty viruses, so caution is advisable.
Sanitizing the water system should be done before using it. I won't go into detail here, there are many references online as to what to use and how to do it.
I'm not sure it is absolutely necessary to replace all fluids (coolant, engine oil, transmission fluid, differential oil, brake fluid (if any), etc.) immediately, but it is probably advisable before putting very many miles on the rig after you get it running. DO, of course, make sure all fluid levels are correct before starting the engine!
Just some thoughts from an old retired mechanic...