Audio Twin Power Feed?

Morning all, I have a camper with a really nice audio system which I am just fitting, obviously this is powered from the main host battery, but I would like to switch the power feed to the leisure battery when I am parked up so as not to drain the main battery, and back again though the ignition when driving. This must be fairly simple but i cannot get my head round it. Cheers Paul

Scenario 1: If your vehicle has a 7 pin trailer connector there should be an ignition switched, fused, battery lead in the harness. Limited anywhere from 20 to 30 amps. Theory is, car is on both main battery and leisure battery connected in parallel. Turn off ignition they are isolated. The downside: you are limited to the amount of current draw by the above fuses. If the leisure battery is too far drained it probability won't fully charged. T would use a DC/DC battery charger that would properly charge the leisure and limit the current from the main battery/alternator. Scenario 2: Install an ignition switched high amp relay and run a fused line from the main battery to a disconnect to the back of the vehicle. This differs from the above situation as you can increase the current available by upping the wire size and fuse. This would accomplish the same separation of starting/leisure batteries. Also this scenario would allow for less voltage drop to the trailer and a little better battery charging. The above limitations still exists.