amperage draw was why we didnt choose to add one in ours.
1st the 120 volts models can pull 75 amps
and the 230 volt models go upwards of 25-30 amps
even a 50 amp rv cord and breaker box just inst going t cover the load
a 50 amp service is two 120 volt lines with 50 amps available on each line, technically you do have 230 volts , but you would not have any power left over for anything else and the park pedastal might just do a melt down
However if your a park model and set in, you might be able to work a deal to get a separate power line off the parks main line and run a you a 230 circuit thats dedicated the water heater.
this being said i did find a few that might be suitable depending on your water flow requirments
this one is 230 vlts and needs three LIVES plus an earth ground. OUCH
120volt 29 amp
if you do decide to do it
please do a write up or MOD for all us Rvers