Hi Lawnlord,
RV furnaces will only run if the blower motor is pushing air at something like a minimum of 75% of full capacity. If less than 75%, it will stop altogether. So if you can hear the blower running, but no air comes out of any vents, it sounds like the air might be leaking out between the furnace and the registers. On rare occasion, duct hoses come loose and fall off the furnace or the floor register. It's also possible a critter has gotten in and chewed holes in your ducts.
You'll probably have to get into the basement where the backside of the furnace is located to see what's going on.