The Hydro-Flame line is from
Atwood; see their
furnace page for details... okay, not much detail, since they don't post much on-line.
I did notice that the
furnace is arranged like a typical water heater, with access from the outside via an access door the size of the whole end of the heater. They're quite proud of that. In contrast, a typical
Suburban furnace has only smaller fitting for the vents. With a flat-sided trailer either is okay, but with a curved egg I would be concerned about how to fit the Hydro-Flame door... my water heater door is in a somewhat awkward "bump" on the side of the trailer. If the old Hydro Flame had the same outside door as a new one, that would be okay.
Atwood's Hydro-Flame Everest Star II has a configuration more like my old Suburban.
If you search the FiberglassRV forums for "Hydro Flame" (include the quotes, to get exactly that phrase) you'll find a few topics regarding this brand of
furnace, but keep in mind that some refer to the old "gravity" or natural-convection design - presumably no longer made - which operates without a fan. Maybe the one which was taken out was one of those?
The FiberglassRV Document Center has (under Appliances) a set of furnace manuals, including what may be the same model as being considered.