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!!