I should mention that fiberglass just really isn't an option for me. Urethanes and epoxies are iffy, but doable, fiberglass, not.
I worked for many years in an environment where the air was full of solvents, oils, etc. I have developed a lot of substance allergies, and on top of that, all those things trigger my wife's asthma.
What I did do was read all I could find about why plywood delaminates, and the reason is always (other than some totally defective stuff) moisture.
So, after looking at all the means of sealing people used here, I began thinking about some stuff I used a number of years ago to fix roof and vent leaks in my old travel trailer. I used this
http://www.eternabond.com/AlumiBond-p/rv-as.htm and was seriously impressed with its permanent sealing abilities, not mention it stays forever flexible and won't crack, etc, because it's not brittle.
Later, I managed to run across this:
http://www.mfmbp.com/productView.aspx?id=1Which set me to thinking that to avoid the UV problems with both urethanes and fiberglass, what one must have is an impermeable, self bonding finish. Still working on that, but the idea is to work on sealing, rather than glassing. That stuff would be perfect for the roof, and depending on appearance, just might be the answer for the sides, as well.
5 out of 4 people are bad at math.