Furnace, water heater, refridgerator, airconditioning systems, etc, were only installed by the RV builder. They were made / built by subcontracting companies, many of which are still making those same systems. The systems you're talking about, are common with a large number of other trailer brands.
Get the make / model information off the particular systems (IE Atwood / Suburban / Etc) you are interested in. Then search the internet for that. Most likely, you will find what you're looking for.
18 Nissan Titan XD
12 Flagstaff 831FKBSS
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