charging battery on camper

Martin, I assume you will also be running a fridge on 12v in your camper while you are travelling. Your camper if already wired with an anderson plug will probably be set up for this. You will need to run a heavy guage wire around (16mm2 which will be the same gauge as is on your plug on the camper) This size cable cable may seem to be rather large but in a 12 volt dc circuit voltage drop will be quite considerable and will be needed to properly charge your battery and run a fridge while on the move. If you are not running a fridge in the camper you wont need such a large wire. You can run this wire from your second battery through a 20amp circuit breaker to the rear of your patrol direct to a new plug. Install the circuit breaker as close to the battery as possible. You can get this cable, (anderson plug 50amp), circuit breaker , lugs, sleaving to protect the wire and any other gear from any good caravan supplies outlet. The cable is 2 core so run the negative directly to your second battery. You should have what is known as a smart solonoid on your patrol for your aux battery, ( common and a must for the 3lt ) when your car is running it wont put any charge into your aux batt. until the main is fully charged. When the main is charged the the smart solonoid switches over and runs charge to your aux and now your camper battery also. It might cost a few bucks to set it all up but if you do it right the first time then you wont have to do it again. Good luck!
smod.