All depends on how much you run. My 5500 Runs the entire coach. 2 A/C's 1500 watt Water heater. Kitchen stuff and of course all the eletronics and fridge.
AND has enough left over to power 3 100 watt Ham Radio stations, lights and computers for logging on field day.
In short. more than I can eat.
I suspect your 4,000 will do so as well. IF NOT.. Switch water heater to PROPANE or.... When I had to replace the tank I also repalced the new heat element with a different one 1500 watts at 240 volts... At 120 volts that is about 375 watts.. Takes a bit longer to heat things up. but... A whole lot longer to trip a 30 amp park breaker and less load on ye old onan.