Adding a second battery before an high output alternator will just put 2x the strain on your stock alternator with the 2nd battery. Big 3, Under hood battery, Alternator, Extra batteries in that order
i had 2 batterys in my path with no probs thats prob cause it came with a 120amp alt. your civic and camaro come with 80 amp alts i believe not to sure i know the civic has a small one. dont think it going to like charging 2 batterys for very long. get a H/O alt do the big 3 and get more batts and 0/1 gauge wire and call it a day