Use 3m weather strip adhesive, it comes in black or yellow, it is a contact adhesive, you put it on both what your going to glue & what it is going to be glued to. Let it cure till it skims over, you should be able to touch it but not get any on your fingers. Then carefully place it where you want it. Then take a rag rub the knee pad pressing on it to get an even surface. You can remove the excess buy rubbing it with your fingers after it has dried or you acetone but be carefull acetone can damage paint.
You can get it at any auto store, possibly at wal-mart too but not really sure. They use it to put weather stripping & moldings on cars & trucks. Where you are attaching rubber surfaces to metal surfaces.
Hope this helps, take care
Stogie
