Try using pieces of sidewall material cut from a worn out 18-wheeler tire. The stuff is as tough as woodpecker lips, and layers can be stacked if a thicker cushion is required.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!