I have been looking into options for heating a 23ft Safari while boondocking that do not require electricity for the fan and also address the issue of catalytic heaters consuming inside air. I came across two marine heaters designed for heating boat cabins that run on propane. The Force10 brand vents outside but consumes inside air for combustion. However, the Dickinson Marine Heaters have two new LPG heaters that combine outside air intake in the vent tube. BTU range is 5,500 - 7,500 for the smaller unit and 7,000 - 9,700 for the larger. Dickinson is located in Everett, Wa. and sells thru various marine supply houses. The web site is ww.dickinsonmarine.com
. They are made with stainless steel & come with a rear mounting plate to protect the surface it is mounted on. One would have to clarify side clearance to combustibles. Both units have a decent size ceramic glass view window for watching the flame for ambience. It comes with stainless vent pipe and deck fitting and cap. An appropriate mounting place would have to be found that allowed venting through the roof. Not sure if the curved roof of the Airstream would present a problem for the vent cap.
As for the bottom line, I think they range in price from $500 - $600. I called Dickinson in Everett and the guy told me they have sold them for use in campers and trailers. I'd be interested in hearing whether anyone has ever had experience with these.