Bill is correct. You cannot guarantee there are no leaks somewhere along the AquaHot exhaust that might cause you grief in an enclosed environment, even if you try to pipe the bulk of it outside somehow.
Try a couple of small electric heaters, although if you're not on 50amp power you'll have to balance them (wattage/amps) with other appliances and AquaHot electric side as you need them. Also consider using any Air conditioner heat pump(s) if you're so equipped. They'll work above 40 degrees F, but below that they can't ferret out any further heat from the ambient air. Again, if you're only on 30 amp power, running even one AC heat pump will require careful discretion when turning on other 120v devices.
Also note that the shorter and heavier any power cords are to the coach the better. If, heaven forbid, you only have 20 amp power in the building, you will be severely limited as to electric heating, so be careful. In that instance I'd not go over 25 feet of 12 gauge (yellow) extension cord, and if close enough don't use an added cord at all; voltage drop increases significantly over length of cord, and 14 gauge (orange) is ill advised. Don't go cheap on cord/outlet adapters either; buy the highest quality, heavy duty only. I speak from 37 years of experience, not all good
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Joel