the whole trd authentic kit is made of polyuretahne
An authentic TRD
Wing is made of Fiberglass...urethane would be too heavy. The rest of the TRD
kit is made of Urethane (sides, rear, front). If you want to get a replica, you should check out spoilerdepot.com. I have heard great things about their spoilers.
I believe that the entire kit is made of polyuretahne. You are right though, the TRD
wing is quite heavy, and due to the increase in weight, the stock trunk lifter thingies
need to be replaced.
As for the hole drilling aspect, the TRD
wing requires that additional holes be drilled in the trunk, and it also uses the holes used by the stock spoiler. The bad thing about replicas is that some don't fit properly with the factory spoiler holes.