My question is how long are you staying? I have used the 20lb bottles for years in the truck camper and never used a full one on a trip, on the motor home I have not even dropped below 3/4 when on a trip.
I only turn on the hot water when I need it and the furnace only when cold. If you have hook-ups you may want to get a 110V heater to relieve some of the draw on the propane one.
If you do need more propane then I would go with a larger tank or if you are parked for long term someplace (months) then get one of the huge tanks and hook up to that.