We've been using extruded fiberglass and Lexan for three years. It's very easy to work and simple tools will do. Extremely strong for the weight.
Non metallic so it is transparent to the radio waves and no grounding or shorting problems due to a metal frame.
Videos at
http://www.phxhs.k12.az.us/education..._id=1127872327
we use it on our ROV too.
Great stuff