Blue loc-tite on the threads will work fine to hold the screw from coming out.
If you're concerned about them slapping off the rim and making noise, you can put some plasti-kote resin around the edges and let it harden up, that will make a (you guessed it) plastic coating on the edge. You could also go to your local farm store and get some seat trim to crimp around it.
Another option is to put the blobs of silly-cone on the pan itself and let them dry so that when you install it, they press against the rim. Rubber stick-onz work well as standoffs too.
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