Needing help, evacuated, battery dead

Jumper cable from starter battery on the RV to the house battery lugs. That should allow you to start the generator. I assume your house battery supplies the power to start the generator. Many possibilities as to why your house battery failed. Maybe your converter is turned off or it has failed and didn't charge the house battery. It also may be your house battery has died or the cables have a bunch of corrosion. Corrosion can run up inside the cable sheathing, especially on the positive side and eventually the cables stop being conductive. Lots of potential problems. But you should be able to jump from the chassis battery and get the generator running. Be sure to Run the RV and keep the chassis battery charged, you don't want to be totally dead in the middle of fire country.