The electrics in TT2 are a little different from normal caravan/campervan installations. I already had a 12v Halfords power pack, and wanted to carry it on-board anyway, so I decided that the camping electrics would be completely separated from the main van electrics - the camping circuits don't even use the metal of the body of the van as the negative return. I am aware that the van battery is quite small, and I didn't want things like the lights/DVD player/water pump/other devices to end up draining the main van battery. Also, as the power-pack is only strapped into the storage unit, it can still be used as a compressor, jump-starter or lamp. Other installations have a split charge relay - a clever box that allows the leisure battery to be charged once the main battery is fully charged.
If in any doubt, contact a qualified electrician to do the electrical work on your van. The last thing you want is to build-in electrical problems - with all their consequences for you and your van!
My installation uses the power pack to run the lights etc in the living space. The pack comes with a mains charger, but can also be charged as you go along by using a connecting cable that goes into the cigarette lighter socket. I keep the mains adaptor plugged into the mains circuit in the van, so whenever I connect to the mains, the battery pack gets charged. If I'm a long time away from the mains, I use the cigarette connection to top-up as I drive along.
The lighting and water pump power supply goes through a small additional fuse-box (purchased from Halfords). All other links to the battery go through 12v extension multi way sockets that have fuses within the plugs. There is a 4 way socket that presents itself on the extending bed leg. This means that when the bed is made up, the socket comes out with the leg, making it easy to use. Otherwise, the socket would end up under the bed!
The cool box plugs indirectly into the cigarette lighter socket, but can also be connected to the power pack battery if the link cable is connected. As it draws a lot of current, I only usually switch it on when the engine is running. I find that it stays cool if an ice pack is used - most campsites now have a freezer to re-freeze it.
The multi-way 12v adapters usually have a small bulb in them to light the unit up at night, making it easy to see where they are. This does put a very small drain on the leisure battery - the more you have connected, the more power they will consume. I took the covers off and disconnected the bulbs. Maybe worth considering if you van is to be left for long periods of time.
Mains 240v System
The mains system has the external connector under the bonnet. That saved cutting the bodywork of the van! It keeps the worst of the weather away from the connection. The power cable then goes into a double socket which has a built-in RCD safety system. As the wires are running within a metal tin, it is essential that this protection is included in the design.
The first of the protected double socket is used for the charger for the battery pack. The second socket is used for a 4-way extension lead which presents itself at the side of one of the bed units.