Been looking for similar feedback, although I don't plan on removing my sharkfin. I just acquired a RTT now my satellite reception is crap. Got a recommendation on a fb group for this:
XM RADIO ANTENNA KIT
Then read somewhere (can't recall know, I've been searching all over) how someone hid the antenna in the plastic spoiler in the back. Sounds like a good option to me. I'll probably just run the wire for the new antenna to the head unit and unplug the sharkfin and leave it in place, then just plug in the new antenna.
