Brake Disc Rotor problems of the 2001 Ford E-150

Purchased the vehicle late 2001 and has been in 6 times for new rotors and breaks due to vibration when braking. Ford has covered it so far, and the dealership just tells me that because the van is heavy in the front that it is a common problem. I feel this is a design flaw in the vehicle. Who can afford a $600. 00 brake job every 4 to 5 months?.

There is vibration when braking, dealer grounded rotors twice so far.

Front rotors warp, and continuously had to have rotors changed every two to four months, causing tires to wear out. Please provide any further information.