Fence posts; interesting example. Makes me consider a cedar board fence bordering one side of my vast estate that has stood for near 20 years, in all weather including one hurricane, posts and all. on the other hand, my end blocks were well encapsulated in epoxy, inside a boat compartment, and didn't make 10 years. I'm dumbfounded as to how they could have disintegrated.

One of the downsides of sealing wood to keep water out is it also seals the wood to keep water in. If water gets in it is hard for it to get out. This is probably not a big deal if the area surrounding the sealed wood is dry most of the time. If the seal is a little permeable any humidity will go from the wetter place to the drier place. But if the kayak is use a lot and there is often water left in the boat and it is in a humid area, it will be really hard for the wood to dry out.

Epoxy is waterproof, but that does not mean it is not permeable. Waterproof means it won't soften with exposure to water. Permeable means it allows water to pass through. Even a really solid coating of epoxy is permeable, but it is hard to get a really good barrier of epoxy on end grain. The grain of the wood promotes small holes in the epoxy surface that will let water soak through the epoxy surface. The surface will sort of be like GoreTex. A layer of fiberglass over the endgrain will help because it helps prevent the holes.