I have a suggestion, have you tried running 2 batteries? you can get a battery isolatoer from your local auto store, the isolator runs between the alternator and the batteries, this will allow to drip to two batteries. Your main battery will run you rengine needs and the second battery (motorcycle batteries or something smaller) can run your toys. The ground for your toys can connect to the ground of the smaller battery rather than the chasis of the car. now you have a battery small enough to fit in your trunk and you have taken off the strees from your main battery to run your gobs and gobs of watts from your amps, speaker box, and cap. Of course, this will add weight to your car and the whole relocating your battery to the trunk idea is out of the window.