When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The gas tank is back there somewhere. Might be better off under the seat. Best bet is the rear of the hatch where the 2LT / 3 LT subwoofer is. If you have the 1LT then there is a large void there allowing the amp to be totally hidden. If your creative there is likely room under the floor of the rear hatch where the factory amp and lots of other electronic in the car are placed (battery, fuses, etc).
To correctly interface with the factory BOSE amp you need one of these OEM integration units:
AX-DSP-MOST1
NAV-TV M650-GM
PAC AP4-GM61
You can do it via a LOC (line output converter) but the results will be subpar as the Bose processing will still be applied to the signal. Thus you really don't want to amplify the Bose signal due to its bass volume problem and noise cancelling feedback issues.