I've seen those too, and wondered whether I could engineer a shell insert for them that could turn one into a good trailer water heater. Standard 6-gallon propane
heaters have a number of disadvantages, not the least of which is they take up a lot of cabinet space and hold 50-plus pounds of water (6 gallons) that can't really be used to drink or bathe in because there's no easy way to get the water out of the heater without pumping more water in.
So a converted instant water heater could save space and weight
. And because it has an electronic ignition you'd never have to worry about going outside to light
it on a cold, dark, rainy night.