I got all excited about a tankless water heater at first, but it doesn't make much sense to me unless we are talking about using the Eccotemp outside. I thought about trying to build some sort of rig to mount the unit outside to feed the water back inside, but that would mean poking holes in the
fiberglass, having to go outside to turn the knobs, plus possibly melting the trailer's hull with the intense heat that exhausts from the top.
There are two actually made for RV installation, and the cheapest is the Girard, at $700. I can't see how it would be worth it. It's the same size as a 6 gal heater, costs way more, and doesn't really buy you that much more hot water for a shower, unless you are fully hooked up at a facility, because you are not going to be carrying around enough water for long showers. In my case, the grey water capacity restricts this even more.