For some reason, I was thinking the alum brackets are a heavier gauge, making them substantially heavier.
Sounds like either fiberglass or alum are viable choices.
The problem with Unlimited is that their website says their online ordering is down for maintainance... for at least 3 months that I know of. I can call them and see if they sound like they're in business. It's not a good sign when a business does something like "temporary maintenance" for over 3 months!