There are possible downsides to relocating the battery to the trunk. Venting. Voltage reaching your starter. Cable size. Apparently that kit assumes you will use your frame as you ground cable contact. Not the best arrangement. If you're talking about NHRA track rules, there's a whole other level of requirements that include a solid fire block between the pass compartment and the trunk, a power shut off that can be operated from outside the vehicle( you prepared to drill your tail panel for switch?), battery tray held down with min 3/8" bolts( 4 I think) to the frame.
How bad do you really want/need it? How much are you willing to do to make it work?
