So we went with a tankless model and have had varying successes and failures with it--The first one wouldnt work, so we sent it back and replaced it (amazon warranty) with another new unit, which worked fine. We figured out that the polarity of our battery had be reversed at some point, so had to buy a new battery to get that to work (the propane heater wouldnt wokr because of the reversed polarity, which probably fried the new water heater as well).
Where we ended up parking we were without a water hookup in the fall, so just used cold water (we were on a severe water-reduction program!). All of our used water had to be transported via 35 gallon gray water tank in the bed of our truck.....we went 4 month and only went through 140 gallons of water! (showered elsewhere, obviously). We found a killer deal on renting a suite at a local B&B, so ended up staying there for the winter and have put off the catalytic heater/wood stove situation for a future project. When we winterized the Airstream, we found that mud daubs were in the exhaust piping for the water heater--We had it cleaned, and it works great. For the water heater we went with the Atwood model.
We did have to replace the rear window (blew out somewhere in Oklahoma) and a roof vent (forgot to close it one morning, also in Oklahoma....). The trailer brakes went out in Memphis, TN, and we had to get all four replaced immediately, which set us back about 2 grand and 14 hours of travel time (we didnt have the tools/parts/space to do it ourselves.....). The rear window we found used, the vent we did with a Fantastic Fan, and the brakes...well, we did those on our journey.
I think we learned that to live full-time in the airstream, it's really required to have a full-time electric, water, AND sewer hookup, and still be ready to live with a light footprint....
Since we've settled a bit here in Maine now, we're buying a house and are planning on using the airstream for guest quarters and slowly finish the renovations over time!