I plan on running it with the car off sometimes (like when waiting for someone w/ the volume down). Isnt it also possible to just ground the 2nd battery and run the power wire to the monoblock?
if thats all youre going to do, it seems like you shouldnt need an iso, and yes, you can ground to the chasis, and run the positive to the front batt, and the amps positive to the back batt.