You said that the water heater is the only thing that runs on propane. So your stove/oven is electric and you have a heat pump/AC unit for heating and cooling - right ?
If correct then I would FOR SURE put in a nice high efficiency electric water heater. Why mess with propane for that one thing ? My electric water heater (Florida) was in the garage. It was pretty hot out there all summer (April - Oct) and still at least 75 or so in the winter during the day so the electric usage for heating water was not bad.
And just FYI in case you don't know - winter is the cheap time of year for utility bills in Florida. The opposite of the Midwest, where I'm originally from. Hopefully that monster big AC/heat pump you have sitting next to your house is a high efficiency unit because it will be running 24/7 during the long Florida summers. It was always permanently 'on' by Easter and never turned off until about November. I lived near Orlando and I still remember being amazed a few times having to run AC on Christmas Day.
Tim