Im not a boat builder and dont know the best solution for your problem...BUT, if i was was dealing with it i would do the following.

Rip a piece of core foam (corecell, Divinycell, etc) on a table saw to about 3 inches wide. Wrap it in glass and epoxy resin. Glue it to the inner edge of the hull creating new lips. Then run a few strips of glass wrapped foam on top of the stringers creating a base for the decks to sit on.

I dont know alot about boat construction so i could be totally off.

MIKE HELP!!!! TheManShed is a true builder and he can point you in the right direction i would think. He has helped me out and doubt he would have a problem giving you some suggestions.

I replied to your PM. Let me know!