Re: Marine Water Heater
I don't believe that Atwood makes a heat exchanger type water heater for the RV market. So if you want one, you would have to go to a marine version.
Most things that are not "approved" for RV use can still be used in an RV. Several years ago, I contacted some folks who made tankless water heaters about whether or not they could be used in an RV even though they were not "approved". The company told me that the company pres, VP and most of the engineers (and many of the workers) were into RVing and had installed them in their RVs quite successfully (these were vented domestic LP tankless water heaters). When I asked WHY they weren't "RV approved" they said it was simply a matter of $$. Too many $$ for a small market segment. To get approved for the RV designation would take years of testing and huge amounts of paperwork, time and $$. Then they would have to market to the manufacturers (who weren't interested as they want the cheapest product they can get by with) and find outlets for the RVers... who weren't all that interested.
So the marine heat exchanger would be fine. Most marine things are fine. There are limitation to the toillets though since some are designed to use sea water and to flush below the water line... plus they are more $$ than a well made RV toilet (like the china Sealand Traveler... which used to be Mansfield Traveler).