I was wondering how necessary is it to caulk the inside of the Vacationer with 3M 5200 as shown on the video since cloth and epoxy is watertight. As well, I have put glass cloth strips on all the seams prior to covering with full cloth so the seams have 12 oz and the rest of the hull 6oz.
The plans for the boats we build were built using a different type of glue then epoxy. That may be why the lans have you caulk the insides of the boat. I caulked mine but used a silicon type caulk which didn't allow the paint to dry later when I painted it. I ended up scraping and then sanding to get all the silicon caulk off before applying epoxy with wood flour to seal and slightly round the inside wood edges. I was told alter in a number of forum posts to never use silicon caulk on a wood boat.
Epoxy does encapsulate wood but I read somewhere that to do it right you have to really seal the edges and ends of wood to ensure water can't get in through the grain. Also if I remember correctly epoxy is not entirely impervious to water. Cracks, small holes, or a dent from where something was dropped on it or slid against it could all allow moisture in. I live in Montana and usually it only takes a shallow hole to get to the hard sandstone layer of rock that covers most of my part of the state. I have found water, when digging fence post holes, in places you would never expect because the rock is layered and if water gets into a crack between layers it can travel miles horizontally. The boats we build are made in layers so a bit extra protection may not be a bad thing.
i used it , but wouldn't again. it is impossible to have it smooth, and it dries hard as a rock with lots of grooves, sharp edges etc. if i ever build another boat, i'd use thickened epoxy to round all the interior corners smooth (although it's impossible to reach them all under the deck. i'd probably still use it under the deck in hard to reach areas.
I general if you use epoxy glue, you don't need to caulk. I mix up a stiff batch of epoxy, with wood flour and just a bit heavy on the silica so it holds it's shape and create "fillets" at the joints. These are smoothed with a plastic spoon or what every tool you have handy. They reinforce the joint, (but probably aren't needed) but most importantly they help when cleaning the boat by eliminating the crevices where gunk can collect.
Dave