I am going to try using some expanding foam - the kind that comes in a spray can. I am going to first cut a piece of plastic - maybe from a milk jug to fit around the mast at the cieling (just to keep the foam from falling out before it cures. I then think I will spray the mast and the opening with some silicone spray or maybe some PAM cooking spray to keep the foam from actually sticking to the mast and the fiberglass. I will them spray the foam into the opening around the mast. it will expand into the opening and then harden in a day or to into a solid styrofoam like substance. If it expamnds above the level of the deck It can be trimmed after it hardens. I will then slide the mast boot down the mast to protect the foam from UV which I believe will deteriorate it over time. When I want to pull the mast - I will just have to cut the foam around the mast and pull the mast up. I can then remove the remaining foam.
