I put a pad of 1/4" vinyl rubber under mine. A section from an old waterski binding would work.   

   I intend to place a scrap of starboard under my mast. 

   My mast foot does not touch the bottom panel. I fit the tapered section to the step so there is about 1/4" gap.

   The tapered section of my mast jambs badly as designed.  What is the best solution?  A thick pad to stop it just short of jambing?

My mast jambs now.  I use a couple of small pieces of 3/4" plywood to pryon and a $2 Walmart flatbar.  I will get around to filing the plywood a bit.  There are mast pads made of rubber and Teflon avaiable at West Coast Sailing.  I use the PTFE jar liners we collect water samples in.  After 4-6 months I dump the water sample and just clean the PTFE liner and silicon to floor of boat under mast.  The fiberglass/expoxy deck should be good enough though.

 Mine does have a gap between floor and mast.  That is now I get the flatbar under the mast to remove it each time.

   I bedded the mast foot to the step hole, here’s how: Tape the foot with packing tape. Put a shim under the step to hold mast off of hull. Make sure mast has the correct rake and side to side plumb then figure out how you can return to that position. Remove mast. Slather the step hole with very stiff thickened epoxy. Insert mast and return to correct rake/plumb. Fill and sculpt epoxy around mast. Let ‘er cure. Pull mast (this might take a flat bar depending on tape you use) and clean up epoxy on underside. I added HPDE slides to the four inside faces of the hole (cut from one of those thin cutting sheets). The process gave me a piston fit and the HPDE lets me slide the mast in and out with a little effort but without a flat bar.