Apparently it is not all that involved adding the Electric Element to a RV water heater.
This is 120VAC 400WATT HOTT ROD Electric kit for a 6-gallon RV Hot water heater.... Looks like an easy install that screws into an existing hole. Available from AMAZON $108
HOTT ROD ELECTRIC KIT I may be looking into one of these to run from an INVERTER from my battery bank for camping off the power grid.
Also some folks like to use the electric element along with the propane heat to get more hot water.
NOTE: Don types faster than I do hehe...
Roy Ken