In essence, that is what I already have....minus the in floor part. I have a Webasto and I have engine heat. None of which is economical to run. I've yet to see someone explain how the hot water heater part would work. What would the flow rate be? Are you talking a regular water heater or an on demand type? I could easily right now cut into a coolant line and plumb an LP water heater. I have heard a lot of skeptics on this. Not yet found anyone that has done it.
This means I would have to have a propane water heater AND an electric one?
[note] I answered my own question. I would think this: http://www.pplmotorhomes.com/parts/rv-water-heaters/atwood-rv-water-heater.htm
with the heat exchanger would cover it all, minus the circulator pump?