My friend had a 1978 Volvo 240 fitted with gas in 1978 2.0 pertol version as until relatively recently Volvo didn't do diesels.
Which was good cheap to run, but little gas coverage for filling up, wore the needles in your carb as no upper cylinder lub and a honking great gas tank, which you can't go in the chunnel with :'( then in a camper where would you put it unless able to replace the diesel tank which is not a good idea i don't think as the whole point would to be able to choose which was the cheapest to run on, i suppose from a cooking heating point it could be worth it mind ???
If it were me i certainly WOULDN'T fit one to my current T4 as it's alraedy built and space is already at a premium although if i ever get teh chance to do my dream custom build i wish for everyday i might as central heating would be a major boon to me with my health, on top of the fact i would be able to hide, postion it far better / easier