Since this is an R-Vision trailer, I'm going to bet the furnace and water heater are Attwood. I had a 2005 Trail Cruiser by R-Vision and around 2013 both the furnace and water heater valves started leaking. If you have an outside removable cover on the furnace, you do not have to remove the unit from the trailer. It is fairly simple to remove and replace the gas valve. I found the replacement valve online for about $50. Be sure to use the yellow gas teflon tape on any fittings which aren't flare fittings. This fixed my problem and no more propane smell.
Hope this helps and happy camping.
Ken