Hi
You could go with an Optima battery,it dosn't matter which way up you mount them.Then you could just mount it to the frame somewhere and not have to cut up the body.What are you using the extra battery for?
Thomas
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews