I have used two 20 amp circuits to power my RV, I had to exercise limited energy management (leave water heater and fridge on GAS only. turn off an AC if I used elewctric Kitchen stuff) but that would be my choice.
However I will warn.. If you "Back feed" an outlet with a generator during power fail that is very very very very very dangerous.. Have a proper transfer switch installed so that the loads (Selected loads as well) are, at your choice, powered by Mains or Generator.
Leave one seldom needed light on the MAINS only. turn it on during power fail and when it glows.. Switch back to mains.
And yes. that is exactly how I did it.