The major controls in an RV LP gas system are the main tank shut-off (may be multiple valves if more than one tank or bottle), the pressure regulator, and, in older systems, a remote control shut-off operated by the LP leak detector inside the RV. Your 1994 Damon has such a remote shut-off. If the LP detector is shut off, has detected a leak, or has lost 12v power, the remote control solenoid will be off and no gas can flow. Make sure your LP detector is turned on and working.
A clogged regulator can also prevent gas flow. Clogs are not terribly rare in old LP systems because oily residue in the LP and condensation moisture can form little blobs that can get sucked up into the regulator. The fix is to replace the regulator and that's not expensive. There is nothing unique about an RV LP regulator - it is a standard unit allowing 11 W.C. inches of pressure and available in most hardware stores, home centers, and gas service shops as well as RV dealers. If a new regulator also gets clogged, it may be necessary to have an LP gas service purge the tank to clean it out. That is rarely required, though.
And of course the main tank valve must be turned on (but you knew that!).
Most modern RV LP appliances do not have primers. They are sometimes found on pilot ignition furnaces and water heaters, but rarely on DSI ignition units.