[Greene]

edloh-
If it feels flimsy you can always beef it up with some additional layers of glass.

Also, now is a good time to eliminate all the 90 degree corners between the transom skin and the hullsides/bilge. Making large fillets and glassing over with some strips of biaxel will really strengthen the outer skin.

Before installing the transom core you'll just have to go over the inner edges of the core with a round-over bit on the router so that it will fit snug with the newly radiused corners.

-andy