As you know, the 04+ WRX's have an antenna in the rear window. The metallic content of the tint interferes with the reception to varying degrees (in my case, no radio, period). So I tore off the C pillar interior panels to get access to the antenna hookup. See below.

Simple enough. I unplugged it, turned on the radio and suddenly I at least got a little reception.
It's dark so I'm done for tonight, but tomorrow I plan on running 18 gauge wire through my wing and making it my new antenna. But I was wondering -- will it be alright to run unshielded wire from there (the C pillar), along the trunk lid (which is, of course, steel) and then to the wing, or should I get some shielded wire to run up to the wing, and unshielded through the wing?