Got one of those sirius tuners for alpines for free and i'm trying to think where to put it for best reception. I was thinking dead center on the roof just before the rear tailgate to avoid any blockage from the racks but looking for some input and tips on routing the wire.

I have mine run out through the rear hatch grommet and then up to the roof. It was fine in the place you describe until I put my custom rack and tire up there. That blocked the signal a few times in certain directions. I moved it further up and actually mounted the magnet on the spin down I have securing the top of the tire.

The wire runs through the grommet, then inside near the tailight assy staying behind the molding. Then under the carpet, under the seat cushion, under the carpet and up at the center console where I have my Sirus receiver installed.