This is on solution I decided to use on my PM.
It is made of Mylar. It is designed to be epoxied to the hull. It is tough stuff and is not suppose to develop a memory. It seals pretty darn tight! Will see how it works
.http://www.apsltd.com/c-6563-centerboard-gaskets.aspx
RE: Dagger board trunk slot
» Submitted by Barkleyboater - Wed, 11/6/13 » 1:55 PM
http://www.apsltd.com/c-6563-centerboard-gaskets.aspx
Corrected Web Address
Have a great build day!