I have not seen the ones you are talking about but why not just use an Aqua-Hot or Hydro-Hot setup? This is what the "big boy" bus conversion companies use. It burns diesel and heats your rig via hydronic water-to-air blowers that you mount in the tow kick area of your cabinets and such. It also heats you water and can preheat your engine coolant.
Aqua-Hot
I plan on using one IF we decide to build a new conversion instead of the 5er we are leaning towards.