I'd suggest acquiring a retired truck tire and using a reciprocating saw to cut rectangular chunks out of the sidewall. Then use a couple of big C-clamps to squeeze the pieces together while you drill holes for the bolts. There will be enough rubber in one tire for several attempts if the first one isn't satisfactory. Vulcanizing everything together is nice, but it isn't totally necessary. I'd also suggest using a couple of small bolts and nuts to hold everything together while you install the mount, and remove them later if they cause unwanted vibrations Good luck!
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
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