One word of warning regarding polyurethane is that is can be "eaten" by mildew we learned this the hard way by leaving a blimp in a trailer during warm weather and came back to it and it was full of microscopic holes.
thanks for the help paul!
huh I never would have thought that mildew would do that, this is a lesson I will keep in mind.
iv also checked out inflatable2000.com but id like to make mine, and im really considering poly. but I want to learn about pvc.
This mildew-would it be a problem for an endurance flight, would it eat the stuff that fast?