I have a Boston Acoustics GTA-1105 amp and where is a good place to install it in my 07 TL? I was thinking under the rear deck.. What do you guys think?

 

Its all personal preference. Depending on the size of the amp, you can mount it in various places.

1. Under the front seats (if its a small amp)
2. Under the rear deck
3. Attached to the back of the back seat.

Then there are more intricate places like false floors, in the spare tire area, etc. I would recommend that you DO NOT mount the amp to any sort of sub box. There have been so many instances of circuitry going bad inside of the amp due to the vibrations. I previously had mine mounted to a box until I did some research. I started freaking out because of the stories I read.

There is a thread on here where people show off their "systems". There are lots of pictures for you to get some ideas of what will work best for your setup.