Putting the plug "in" the table to make a half mold.

After the plug is primed and sanded (and primed and sanded ...) I created a table

to drop it into, to create the mold flange. I put the plug on the surface and leveled it
then using a right angle drew the outline. After cutting out the center and making a
close fit I coated the surface with epoxy. Now you can drop (lower gently) the plug in
and level it. To fill the gap I used modeling clay, this may not work for you if you
live in a hot environment. All surfaces have been polished and waxed prior to this point.
But more wax will be need before the PVA is sprayed.