I am on my third VW van, the past two were campers. for about $30 I built a rack system out of 2" pvc. I have the best of both worlds, transporttion for my kayaks and overnite accomodation all in one. By putting a "T" in the middle of the rack i can screw in a 2 foot piece and stand my fiberglass yaks on their side, allowing me to get 6 of them up there. And up there they are about 6' up, small price to pay. I bent some flat stock and mounted them to the side of the pop top and the pvc slides over this, thus allowing me to remove them when not needed. My vw gets about 19 mpg. however, i know more about repairing a vanagon than i do about building kayaks and i've got one wood strip and 15 fiberglass yaks under my belt.