Have to add my 2 cents.  First time out in our recently purchased '85 
Westy camper was a trip from Cape Cod Ma to Baltimore MD.  This camper 
had sat unused for over 15 months except for an occational test drive 
because it was up for sale (but barely running).  With a mega-tune-up, 
new belts, hoses, filters, gaskets, oil & filter change, transmission 
filter/fluid change, 0xygen sensor, coolant sensor etc. and I'm sure a 
few other things I've forgotten, we got an average of 26 MPG.  We had to 
watch this very closely because we had never driven it before this trip 
and our gas gauge was broken.  Our camper has automatic trans and 207.000 
miles on it!  A little over 105,000 on the second (R/B) engine the PO had 
done.  So it can be done.  We get about 17 in stop & go around Cape Cod. 
The first trip was fully loaded for camping.  When I learned how to drive 
(many moons ago) my driver ed teacher had an uncooked egg placed between 
your foot and the excellerator.  If you broke it, you paid for that 
lesson over again until you got it right!  Must have worked.
Wendy
'85 Westy
"S-Cape"