More efficient propane furnace

I know my camper isn’t insulated like a house, but the furnaces in RVs seem unusually inefficient, even crude. It does seem like someone would improve on what is essentially thirty year old technology. My unit is in fact 18 years old. And it was no state of the art furnace when new. Someone mentioned a two stage unit. That sounds very interesting. A better heat exchanger seems possible. I know two stage units in houses do have greater efficiency. Anyway, every time I get home from boondocking I complain to myself and just thought I’d share my complaint. Does anyone know someone who makes a two stage furnace?