We camp with our camper. We do not 'RV'. Showers are for RVing, where you are on the road. Camping is where you are out in the woods, where a sponge bath and helping to wash each other's hair every 2 or 3 days is plenty.
I have a hot water heater. Nice to have, but I wouldn't get another if it were on the options list. I can heat water just fine on the stove for washing up.
If I am out camping for longer and need a shower, there's usually a shower at one of the RV parks or even some campgrounds for a couple bucks or so. Most times when I get that rank, a bar of soap and the lake or stream I'm camping at will do just fine. Very invigorating!!