I struggled with mine for a couple of years, and a couple of experts 
until I was told that the instructions that DOMETIC gives for lighting 
the thing are wrong!!
To make it really easy, start the frige on 12V and run it around 10 
minutes (110V works just as well) to get the air column working. That 
brings fresh air to the combustion chamber.
Next hold in the override button FIRST and keep it in - take 10/12 (or 
more) strokes on the pump and then beginn  to push for the igniter. Push 
frequently (but not more frequently than about once per 3 sec - spark 
will be weak otherwise) until the LED comes on and stays on. Let up on 
the bypass and it should remain lit. 
After I was told this, lighting mine went from a sometimes week long 
series of frustrations to a quick light. Seems to work just about every time.
BTW - mine is an '86, and there are newer versions in the later year 
Westys - some with automatic ignition. Yours might be different, but I 
think the principles will remain the same.
Good Luck - Jack