This may be crazy, but could you put a bulb on the bottom? Granted, the hull won't be perfectly fair with the bulb up against it when the board is raised, but it might give you the extra stability you're after.
Perhaps an indention in the hull could be made to accept a bulb?
Otherwise, just making it out of a heavier material may be the way to go. But remember, they have to have the strength to raise it.
S/V Old Shoes
1973 Pearson 30 #255