I built an Yare kayak and only glassed the outside and epoxy seal coated and varnished the inside. I went to a lot of effort to get a nice finish on the outside. I have discovered that the epoxy varnish does not maintain, over time, a water tight barrier. I have a wood stain that has shown up in the deck near the front bulkhead and it seems to follow a small void in the luan plywood. I have concluded that a little flexing of the deck will crack the epoxy only coat and let some moisture in. So both sides should have glass, even if you use a light weight layer on one side, to avoid get internal moisture in the wood.

I also built a strip canoe. A lot of walking (compared to a kayak) takes place in a canoe and I can feel the bottom of my canoe flex under my feet. The glass does add structural strength to strips (or plywood). Because the glass is much stiffer than plywood and is on the outside of the structural sandwitch, it carries most of the bendng stresses. Leaving the glass off one side of the sandwitch construction would require the weaker wood to carry the bending stresses and would not be nearly as strong. So my advice is to full 6 oz. glass both sides and add a 6 oz. football to the bottom of the outside. That's what my canoe has and I would not want any less.

Dave