We own the Coleman portable hot water unit you mentioned. We are very pleased with it. Works well once you get use to how to control the settings. We converted ours to attached to 20lb propane tank. much better than using those small cans! We use in our sauna as will as on our boat. On board we keep it below and take it above when we want to use it. Attach to the 20lb. propane tank which we usually have out BBQ attached to and away you go! We put the intact (pump unit) in a plastic storage box you can get at walmart. Just remember they say not to use untreated water! So no lake water or salt water unless it has been filtered first.We stock up on water at various marinas we visit. It is amazing how little water you use with this unit.
You can also use it to do dishes! Good excuse for me not to dive into Lake Huron when the waters cold...brrrrrrr!
We can use it all summer 9 2 months without charging the battery.
Good luck, Allan