When I installed my exterior post lights I needed to be sure that the wiring connections would be sealed from any moisture intrusion. After I soldered the connections, I use a product called Liquid Tape to coat them before adding the wire nuts. They have been over ten years under ground with no problems so far.
While using it, the thought occured to me to try it as a coating to a pair of drive wheels to increase adhesion. As soon as I get my test oval up and running I am going to try it on one of my BLI I-5 Hudsons which need to be able to pull 18 HW passenger cars.
Its a lot cheaper and nicer sounding than Bullfrog whatever.