Yes, I replaced our old 16k Suburban with a new 20k Suburban. At the time we were unable to get a 16k btu replacement. Not sure if they are still available -- probably so.
One problem I had was that on the old unit, there were two 4" adapter rings on the left side (as you face the furnace from inside the trailer) for attaching the two 4" ducts which move the hot air to the front of the trailer, coming out at the floor near the refrigerator, but on the new unit, there was a 4" adapter ring on each side of the unit. I had to fabricate a small collector box on the right side between the furnace and the shower wall, then reroute one of the ducts over the furnace to the collector box -- a bit of a job, but it works great. Since I had the refrigerator out, I went ahead and fabricated all new ductwork and exhausted it in two different places, unlike the previous one.
I could have used the old exhaust vent (the one on the outside of the trailer) but it was quite corroded (it would have fit), so elected to use the new stainless steel one that came with the new furnace. Got the furnace at Palomino.
Good luck with your project. Geo...