: Have been slowly raising the funds to start a SeaTour 15 yost build
: and finally got to buy the marine plywood, 16' (few lil knots) . . .

: I want to protect the wood enough for at least 5-6 yrs w/o , , ,

I don't have experience of oil on boats, but the important thing is how the boat is used. In that case of a SOF kayak the boat will hardly be left unattended in the water. If it will be paddled primarily for day trips and stored under cover then the coating only has to resist the elements for a few hours at a time so anything that will slow the entry of water will be fine IMHO. For tripping, something a bit more durable is suggested.

Titebond III is barely "waterproof" according to reports and my own tests, and is certainly not in the same class as epoxy. If saturated it will soften but if the joint is not broken it recovers all or most of its strength after drying out again. So keep it reasonably dry or use epoxy. Epoxy retains strength when the wood is saturated, I understand.

I use T-3 but not where a joint is continuously exposed underwater. It works well, is easy to use and is perfect for laminating. Used in my small sailboat, protected with regular house paint (Bristol Finish above decks) it has withstood 12 month exposure to the elements in Ontario, Canada for a couple of years now and is still going strong. Used properly it is stronger than the wood, but useless for end-grain gluing (epoxy is only a little better).