Some of the minwax fillers I've seen have been very soft and took a long time to harden...if ever. I really don't think that is what we are looking for in a filler for kayaks. There is a lot of searching for the "best" filler. I know some people have used RockHard wood filler. I have...but not for a kayak. I will try it for that some day. Most of the time I just use wood flour mixed with epoxy (I precoat the wood to avoid color blotches). If you haven't fiberglassed your hull or deck then you are not in too bad of shape for the fit. It is important to try to keep the deck and hull in the correct shape as your epoxy/fiberglass cures. This must be done while you do both sides. You can use spreaders, straps, forms, etc. to keep the proper shape and fit. Even then you may get a little movement, but it can usually be taken care of with straps, tape, etc. while you tape the deck and hull together.