Brake Drum problems of the 2000 Volkswagen Eurovan

The vehicle currently has about 71,000 miles. On 10-9-01, it was inspected by mcnevin vw in berkeley, CA at 65,456 miles. The front brakes were said to have 80% remaining and the rears had 70% remaining. I took it to an independent mechanic at 70,558 miles and he said the front had less than 50% and the rears were at 20%. Since I've owned the van I've had the brakes replaced twice with the third today, 11-29-01. I called the berkeley dealer and he referred me to vw of America. The latter refused any assistence or information why this has happened so often. When I was notified the car needed new brakes at 27,866, I asked why so soon. The answer was that the camper conversion was too heavy for the existing brakes and I should expect to replace them at least every 30,000 miles. This wasn't revealed to me when I purchased the vehicle. The next change was 26,030 mile later. Now they need replacement at 16,800 miles later. The independent mechanic has used all certified vw parts. Approximately 60% of my driving is long distance freeway with little braking. About 40% is city driving at slow speeds with no panic braking. I do not drive with my foot on the brake and am very conscious of using the brakes because of the problem. I hope you can give me some direction in trying to find a reasonable solution with this other than selling the vehicle. In less than two years I will have spent approximately $1,800 for new brakes. Thankyou for your help.