A few years ago a freind of mine gave me a primitive sort of "gauge" for 
a 20# upright propane tank. It was just a narrow strip which was stuck 
vertically onto the side of the tank. When a cup of hot water was poured 
down over the side, the strip changed colour indicating the level of 
propane remaining.
 
I don't see why this wouldn't work for Westy tanks despite the odd shape.
Now if anybody out there knows a source ? My freind just went to sea a 
few days ago and I doubt if he would remember where he came across this " 
gauge" in any case.

Phil Menchions
'89 Westy "Ivana"