I am not familiar with Smith's epoxy sealer, but have precoated the interior of several S & G boats with resin. Lots of resin, as in glossy finish thick, will stiffen the plywood and make it difficult to form the sweet curves when going 3-D. I roll on a thin coat, then when it is cured hit it a lick with #80 grit to give ensuing epoxy work a tooth to grab on. Some decry the "secondary" bond of joints on previously cured epoxy that has been mecahnically abraded but I have never had on efail, and many of my prior builds were outboard race boats.    

I sealed the inside hull panels and frames of my Kaholo with varnish

Thanks guys for your thoughts, I can see where a thick coat would restrict the bending but I thought the kaholo only needed one light coat on inside parts. Thinned varnish is an idea.

Here's my thoughts on sealing the inside of the Kaholo or any wooden boat with sealed compartments. Once you put the deck on you will never be able to get to the inside of the thing again. If you don't have everything completely sealed there is a chance that water, or even water vapors, will be able to get into the plywood. Then the board gets hot on top of your car. The water will eventually show up as an ugly stain on the outside of your board and there's nothing you can do about it. So the best way to absolutely seal the inside of the board is with epoxy. It won't add that much weight if you roll it on thin and make sure there's no pooling in the bottom. Doing it any other way won't be as effective. Especially with something like a paddleboard with some flex properties, it's possible to develope a hairline crack in the finish that would allow moisture in. The Kaholo's will always be breathing a lot of moist air. Hot board, cool water, it sucks in a lot.

George K

I do not see any reason you couldn't seal the wood ahead of time but keep in mind that when you have the hull set up for tack welds and fillets, you will have a bunch of leftover epoxy glue in your hand.  Add a little more resin and use it up sealing the interior.  No fuss no waste.

Lots of good points, looks like epoxy is the best way to go for the best quality job. I'm not really worried about building a heavy barge, don't intend to race, only going to use it for recreation but still want things right, thanks.

Epoxy is definitely the safest option for sure, I went varnish as i was trying to see how light I could go. I also used polyurethane glue for non structural glueing eg gluing deck stiffeners in to frames, fin box block

I also used alot of polyurethane glue on my last project. I did a bunch of samples with the  glue I used on scraps and then tried to rip them apart. I was really impressed with the bond, on okume to mahogany glue ups the outer ply would still be stuck to the board when it came apart so the wood failed before the glue joint. Picked up all my wood this past weekend from Boulter plywood and will get my fiberglass and epoxy supplies this week from a system 3 dealer in town, might start cutting blanks this afternoon.