Ax wax stated above, take something like Jack the Gripper and coat the tires lightly and seal them in a plastic bag the night before. In the morning the tires should be dry again, but much softer. More front caster may help corner exit, on one very low grip track we were running 8-10 degrees. Harder fronts, stiffer front spring, a bit of toe in, less camber. You may even need to stiffen your overall set-up. Nothing is worse in a low grip situation than allowing the chassis to drag. You could also add an extra lip spoiler to the back of the body, and mount the body slightly rearward. You're trying to make the car understeer. Do what you have to to max out the rear grip, then add steering back in to balance the car.