If your relocating the battery to the trunk, make sure that you mount it securely in a leak-proof battery box that is vented and will contain any overflow acid. You should use size 0 welding cable or better that runs from the battery thru the trunk floor with a rubber gromet to protect the cable where it runs thru the floor. Support the cable along the way to the starter with cable standoffs.
Make sure that the ground cable is run from the battery to the frame and that is grounded properly. Also make sure that you have a ground strap running from the frame to the body and the body to the engine. To make a good ground lug connection; grind off any paint and undercoating around a bolt hole that in the frame, stick a bolt at least 3/8 thick and 1 1/2 long thru the hole with a star type washer on both sides, tighten it down, add a flat washer, the looped end of the battery cable, another flat washer, and then a nut that is tighten down also. Coat the bolt with anti-seize to eliminate corrosion. At the engine and body end, grind off the paint and apply the anti-seize to the bolt in the block and thru the body panel.
If using a plastic battery box, make sure to use large flat washers and at least 3/8 bolts to hold the case to the floor. Make sure your battery fits snug in the box, at closed cell foam to take out the slack, and make sure that you snug up the hold down straps. Even though the battery is out of sight, check it a least once a month. Put felt battery washers around the terminals. Clean up spilled acid with baking soda. Keep flammables out of the trunk area NOW!