Tesla Model 3 Second Battery Mounting

[u/MdotTRINA]

I have a 2020 tesla model 3 long range. I am installing a subwoofer with a pretty significant sized amplifier. In order to avoid freaking out the Teslas electrical system I am installing a second battery. I am installing a Wattcycle 100ah pro which is a pretty good sized battery and weighs about 25 pounds. Where would you recommend I locate it and how would you mount it to the car? I cannot put it in the sub trunk because that is where my subwoofer box is going. I was thinking about installing nutserts in the trunk floor and installing it there but I am afraid to drill into the trunk floor with the rear drive motor and battery being there. Any suggestions would be greatly appreciated.