I finished putting in my all fiberglass bulkheads today. I ended up making them out of 1.5 ounce epoxy mat and 5 ounce tight weave. They seem plenty stiff. Picture below of the rough fitting.

The best part is the weigh around 4 ounces each. That's pretty darn light!

They are more flexible than plywood or cedarstrip bulkheads and to me that's a good thing. There is less of a chance of producing a stress riser in the hull that could lead to serious damage to the hull in the event of a hard hit. I plan on using this boat mainly for my significant other's rolling, but also, I imagine it'll be used in rock gardens and surf, so a big hit is definately a possibility.