Plus, the electric element will be on only a short time to heat the water. We have not had any problem with our 30 amp service running everything at once with the exception of adding a toaster or waffle iron to the group. We run the ac, frig, water heat all at the same time.
Never turn the propane off and it is on for the frig and water heater along with the electric. Have yet to use a 30# cyl of propane in the last 2 yrs and spending around 7 months total camping 24/7 those 7 months, so propane cost is very minimal. $15/yr or approx. $0.15/day.