putting the battery in the trunk is always worthwhile, but do it right.
Buy high quality, hi-strand count cable #0 or #1 for the power
( Taylor has some premade 25 ft long , about $55.00)
Add a shutdown relay kit ( about $39.00 )
bulkhead terminals and or grommets for all pass-thru's
May as well install charging lugs in the spare wheelhouse.
And to be legal, a switch to cut power, external to the car.
Last but not least, a solid battery box, no a marine box with plastic strap is not legal or safe, must use a retaining system with a min of 2 3/8" bolts thru floorpan, or welded frame, check out the stock-car parts houses for simple low cost stuff.
I have about 250.00 invested so far ( not counting a no fume Optima ) And I still have not custom fabbed the mount box.
Oh yeah, don't forget to check out John Spina's site ( caspers ) for all the little terminal goodies etc.
My O2, leave the battery where it is, buy a good used GN Front mount I/C, save some money and do it right the first time.
This is not a cheap hobby.