I realize that this is not an option for this boat, but it is why I use polyurethane glue (Gorilla Glue) for stripping hull and deck. It foams which does a great job of filling gaps. It also has a longer working time, so that you have longer to position strips on a boat. The only filling I ever have to do on the exterior of a hull is take the bottle of polyurethane and press it tightly against an area where there might be a small open triangle at the end of a tapered strip and squeeze. Once set, the foam is very easy to carve with a knife or chisel, and it is very easy to sand or scrape.

Beyond that it is not a thermoplastic so it doesn't get a cloudy appearance under the epoxy when the deck is exposed to a long hot afternoon sun. Epoxy adheres to it, unlike a PVA.

Downside is it takes longer to set up. so it may be slower to build a hull or deck. It doesn't make much difference to me, because I am frequently putting on a single strip either before or after work. It also will turn your fingers black, for a few days. I get around this by rubbing in abrasive GoJo hand-cleaner right after using it, and that gets rid of most of the black. It also doesn't have a long shelf life. I buy 8oz bottles, no more than two at a time.