The air conditioner decides this one. Pick your AC and what else runs while it starts, and get an honest generator size.
A 30-amp RV can only accept 3,600W from shore or generator power no matter how big the generator is.
How it works: the moment that matters is the AC compressor starting while your other loads are already on. A SoftStart typically cuts that startup surge by more than half, which is how people run 13.5k AC units on 2200W generators.