Thanks to all who responded regarding my recent propane snafu. The list has spoken and the answer is:
Westy tanks, for that matter all tanks attached to a vehicle, don't have to conform to the 12-year rule.That is for BBQ tanks. The guy who tried to fill my tank, 17 years old if he was a day, didn't know what he was talking about. And the reason he couldn't get propane into it was that he didn't open the fill valve all the way (even though it says "open all the way" right on the valve.) 

Then I took the Westy to another dealer who opened the valve all the way at my behest. He was able to get a half gallon into the tank before the propane starting shooting out the fill valve. Which makes me think all is in order but that the tank has been mostly full for years. The previous owner said she had never used the stove/fridge and she had the van for four years. Is there a statute of limitations on propane, IE does it go bad like gas?

Thanks again,
Bob W.