> That's what the owner's manual in my 90 Westy says too... 13.2 gallons...
> but I measured it closer to 10 gallons.

If I fill mine from the top (by far the easiest way to fill from gallon jugs), I can get around 13 gallons in, but then it spills out the exterior filler on cornering.  I don't think I could get that much in from the outside.  I usually stop at around 10 gallons, to avoid washing the left side of the van as I drive! (yes, I am missing the locking cap for the filler)

Bill