An Aqua-Hot system is a must have for us too. Our previous coach had the up-graded Aqua-Hot where we had the two stage electric feature (two heating elements).
If it wasn't too cold out, we could heat the Aqua-Hot electrically and then turn on the 'fan' system to heat the coach (worked well when in the upper 40's).
You just can't beat the endless hot water capability. We had ours serviced every other year and it was a very clean burning unit, very little smell and virtually no smoke. You must get someone who knows the system to service it correctly.
Our new coach has the Webasto/Espar system which is similar.... ours has 83,000 btu's.
I would want the system to run off of the main tank which is most likely diesel. That way, you will pretty much have endless fuel too.
With the new coach, we were in a cold area for one month (below freezing almost the whole time). We used about 110 gallons of diesel and stayed toasty warm. Since we have a 230 gallon fuel tank, I still had half of a tank left on departure.
MM.