Bracket a piece of 4" diameter steel water pipe securely between the frame rails as close to the rear bumper as possible. Drill a few holes in the top. Pour it full of melted lead wheel weights. That will be about 500 Lbs. worth. Instant traction and improved braking ability, as well as a softer ride.
Jerry
How about filling the pipe with fine lead shot and add a cable operated dump valve so you can lose some weight quick like once the race gets started... I mean for when you need to reduce weight so you can haul heavy freight?