I use the sandpaper method, which is actually emery cloth. It comes on a roll and works pretty nice. Helps keep the engine from sliding as well. The frame looks nicer too when it comes time to sell. You can also use adhesive backed non-skid tape, which looks very similar and is available from a hardware store.
KartLift Kart Stands
DeepSeat Kart Seats
Don't bother PMing me, it doesn't work. Email is best: firstname.lastname@example.org.