And another :

"Gary, I read with interest your post about aerodynamics . I have
experimented with systems for improving the milage on my 85 westy
for 5 years. Results so far are...consistant 23.5 mph at 1000 feet
or lower on the highway at 60 mph At 3000 ft it gets better and
above 5000 ft we have seen up to 28 mph ( on 4 straight fillups)
Denver to Seattle...We achieved this by going to 225-15's tires and
a bustle at the rear to aerodynamically reduce frontal area. We also
covered the luggage rack at the top front and added an air dam
similar to the one on the 87 vans. We have run the system for 50 k
and have really been pleased. Unfortunately much of our traveling
has been in Mexico and the bustle is useless at speeds below 45
mph. Bob Parsons, Texas 85Westy 2.2 Subaru"

Gracias,
 Miguel