khupp: research "dual battery systems", "battery isolators" and of course, "Anderson plugs" on the Internet. There are loads of good resources and lots of pictures to make it simple.
In a nutshell, dual battery systems are composed of the starter or main battery (your vehicle main battery under the hood) and a house battery for your fridge and any other goodies you want to use when your vehicle is not running. The starter battery is designed to always be close to full charge; it does not like to be discharged and it will let you know if you do this. Plates will become sulphonated and the battery will never hold full charge again so don't let it drop charge. The house battery is a deep cycle battery that is designed to be run down and recharged many times; it's not good to go too far, maybe down to about 20% of the full charge or around 10.8V. Full charge is around 13.5V or a little higher. Size matters so if you have lots of goodies go with a big amp-hour battery; 105Ah is good for most 130Ah for heavy duty. The fact that you are asking about isolators concerns me; is your house battery a deep cycle one?
An isolator can be really expensive or really simple but its purpose is to make sure the main battery is charged preferentially by the alternator and once it is charged, it will then charge the house battery when the vehicle is running. It also prevents the main battery from being discharged through to the house battery when the vehicle is shut down and you are using your goodies. Isolators are usually placed close to the main battery.
If you want the option to use your house battery as an alternative vehicle starter, there are isolators with bypass switches that allow you to directly connect the two batteries just for starting. If you choose to do this, you must use thicker gauge wiring between the main and house batteries and ensure that there are adequate fuses on the live, +ve cables to prevent damage to batteries and cables. You also need to choose an appropriate deep cycle battery.
As for Anderson Plugs, they make attaching and removing things easier and are a much better option than your RV plus as stated by others. If you go the dual battery route with starter option for the house battery, I would recommend directly attaching the live and ground wires from the main to the starter battery via a fuse or a circuit breaker on the +ve. The size of the wiring depends on the length of the wire and the current running through it so current will depend on your vehicle. There are tables on line to help; for example a 200A draw for start and a 9.5' cable length would require a 1AWG wire.
If you only intend to use the house battery for goodies, calculate the maximum draw in amps, measure the length of cable and use a table to calculate the wire size.
I hope this helps. There are many examples of really good systems on this forum and the Internet.
