Hi Charlie,

If I were to guess it's probably got an oil base and won't work with epoxy. You have all the materials to do the filling already why go buy something else. My experience is the best thing to use for filler is wood. Fill the big gaps with little strips and scraps that matches the hull/deck and leave the small tight gaps to be filled during the resin coat. Filler of any type shows and is sometimes a pain to deal with during the sanding stage. Hope this helps!