I had a great deal of trouble priming my Webasto heater on my C-34 after it ran dry of fuel. After fussing with the manual's recommendations, and various other sources of advice, I found a simple and easy solution. I disconnected the fuel hose just after the filter and used a hand vacuum pump (like used for bleeding brakes) to pull the fuel through, then reconnected the line and disconnected the one just beyond the fuel pump. I also vacuumed this line, gently while the heater was turned on (to work with the pump and not damage it), and voila!, it was primed. I had spent 5 minutes on it, versus the 2 unsuccessful hours using the manual's procedure (which entailed disconnecting the pump wires and manually connecting them umpteen times to pump the pump- takes forever!).
Jon, nice idea, thanks for posting. Where is your heater located? Any pictures? (http://c34.org/bbs/index.php?topic=3701.0)