I did this quite a long time ago.
The first location at the rear was in the deep well using a plastic battery box from Moroso.
Did´nt like it, took up too much valuable space.
So I measured up the space taken up by the spare tyre.
Tight fit but possible.
This time I bought a Summit aluminium battery box and this is how it ended up.
Using MadElectrical´s kits I relocated a remote solenoid to the rear as well making the thick battery wire to the starter dead after cranking.
http://www.madelectrical.com/catalog.shtml
START'M UP kit (part # ST-1) Remote starter solenoid conversion for GM
Trunk Mount battery helper kit (part # TM-1 & # TM-2) It provides the correct wiring, terminal block, and Fusible Link for installing the START'M UP kit solenoid in the trunk