A lot of manufacturers disappeared , over the years, the fact that Gulf Steam is gone could already be priced in.
Major systems manufacturers are probably still around; fridge, furnace, water heater and other components , should still have parts available.
Access to things , like , wiring diagrams, is probably the biggest issue.
No mention if chassis is Ford or GM, all parts for those are still available.
If the floor plan works for you , and the overall condition of the unit is good, I would not be afraid of it.