Underneath the dash fiberglass?
Not sure I understand - and I don't recall much from the manual other than a pic I saw showing it where I put it ultimately. Our 08' TT has the pucks all lined up fwd of the windshield just behind the wraparound seats via velcro. 2 for the ZO and 1 for the SG. Both are the same Garmin antennae with different stickers.
On my 07' TT 197 it took me 5 minutes to pop the dashpod up - pull the antennae wire through, and resecure. All told - physical installation took about 10 minutes. No issues with a mini tower bimini extended.
Be sure to grab all your baselines and other discrete values out of 6.5ng before you disconnect it from power/display.
The newer version takes zero input from the PW. I now have that version. If you ski on a river with a current, you might miss 6.5ng or the PW version of SG.