hey man...sound pretty good. i think it shold work...do you have a place to get supplies? If not
here , this might help. They have everything you need, including the urethane foam, and its fairly inexpensive...and if you keep it fiberglass you shouldnt have any problems with your plan....
Good Luck....just make sure you get it down right the first couple times...it can get kinda pricey if your not easily satisfied!
let us know how it turns out for you!