Often we have customers put a second battery in their vehicle. I usually suggest a battery switch, or a battery isolator. The battery switch can manually switch your secondary battery on. One of the best i've seen lately is a boat battery switch. With this you can choose battery one, battery two, or both. Drawback is that you have to remember to switch to the secondary battery occasionally to keep the battery charged. The battery isolator will let juice flow in to charge the battery, but will not let juice out to start the battery. You will need to jump from one to the other, but it is always charged. If you go with the isolator, hook all of your accessories to that. A radio left on may drain your secondary battery, but your starting battery is still fresh..

thanks for the info, just copied it off.
I have a regular camping trailer, and it is stocked, just hook on and go.

You can hook two batteries in parallel with a switch between them. Put a diode (rated for higher amperage than the alternator) across the switch with the anode toward the primary battery. This will allow the secondary battery to charge but will not allow it to feed power back into the electrical system unless the switch is closed.

thanks, i had no clue about this either.