If your tires are older than 5 years old by imprinted date codes, they should be inspected for side-wall cracks and probably need replacement for safety, your safety and the underside tanks, wiring and propane lines of your rig.
The house and starting battery(s) probably need replacing from sitting discharged. Brakes and engine cooling system need service/repairs for safety and reliability. Your entire 12 volt dc and 110volt ac system need checking including operation of your converter charger and fresh water pump/plumbing including all faucets. Try starting generator with a good fully charged house battery and use the start switch on the generator itself. Sounds like the generator starter mechanism is stuck and increased voltage might unstick it.
There is a way to turn over the generator manually to free it for starting but I forget how. Make sure the generator oil level is ok. I would not attempt to drop and remove the generator myself and would pay the big bucks to have the generator serviced/repaired as needed. Removal for diagnosis and repair costs over $300 alone.