Just as a comparison, we live in CA in a home that was all electric for the first 36 of our total of 38 years here. (We recently added a propane fireplace and switched the kitchen cooktop from electric to propane.)
Our electric bills for those 36 years were always into the high rate tiers every month. Even then, we never had $800 electric bills for our home's summer air conditioning or winter heating. This is including keeping a 1500 watt heater turned to about 55 degrees in the motorhome during the winter months while it's in storage in our back yard.
Something is definitely wrong in the OP's situation. Perhaps a "leak" in where the RV's main power cable plugs into the residential power, such that extra current was flowing over what the RV was consuming whenever they were plugged in?