You can also mill the extruded fiberglass if needed. Just set up a Shop-Vac with the wand near the endmill. It's only messy if you allow it to be.
We used extruded fiberglass for arms back in 2000 but they never made the final cut. During the sixth week we found a problem (you know how that's always the best time to find problems
) with our arm, not related to the use of the fiberglass, that caused them to be scrapped. Due to the cost and time constriant we didn't order more and went with extruded aluminum we had on hand. I don't have any photos of those arms otherwise I would have attached one.