[PaulK]

It sounds like you will need to take the actual shape of the pieces from the boat itself, and will have to wait until you can get to the boat to trace what is there now and measure the thickness of the slats. Using the “scrim” or veneer to hold the pieces in their places relative to each other does make sense, but I worry about it splitting apart if the whole assembly is glued down with the scrim side down. What if the scrim was stapled or temporarily glued on top of the slats instead of underneath them? The scrim would still hold the slats in position while they were glued directly to the fiberglass, and could be removed once the slats were solidly attached.