I took a 91 fleetwood Coronado on a trade. It has been sitting not running for 2.5 yrs. I had to change the fuel pump and clean tank and now it runs good. Few problems: first Is I can't get the interi...
I too believe that replacing batts will be first. As stated, if they are bad, 12v in general will not work.
Is there a boost for 12v to cross over from engine/chassis to house? This might get the gen started. You may need to disconnect the house bats, if bad. Is converter or inverter/charger working? If plugged in, and working, that would give you 12v (14+) to start and test genny.