Quite a few of the newer people in here have asked about getting a power wire from the battery to the boot. The key bit here is how to get it through the firewall between the cab & engine bay.
Your best bet is to first remove the glove box. To do this simply open the lid and pull it out of the metal hinges. You'll then need to remove several screws around the edge of the glovebox (don't forget the two that also hold the hinges on). There's also a screw inside the glovebox above the manual holder.
Behind the glovebox you'll see a big black plastic flat bit with some wires going through the centre. To the bottom right of this is a rubber gromit. Here's the scary bit: after removing the gromit you'll need to drill a hole through the plastic behind the gromit. The hole can be quite wide and there's nothing immediately behind it in the engine bay so it's fairly safe, but don't drill further through than you really need to.
Once this hole is done, you can pass a cable through it into the engine bay. Make sure that you put any wires through the gromit and replace the gromit to keep the seal watertight.
To get the wire into the boot, firstly run it under the carpets. This can be done by pulling off the rubber seals around the passenger door and pushing the wire underneath the carpet.
To get the wire behind the back seats it's best to remove them. There are two bolts under the back bench. With these out you can just pull the bench off. Then there is a single bolt holding each seat back in place. Again, remove the bolt and pull the back upwards then out. Simple!
You should be able to see that you can pass the wire into the boot through the corner between the bench & back.
Here are some pictures that will help...
1. Behind the glovebox. You can see the thick red power wire going through the gromit.

2. Close-up of the hole

3. Where the wire comes through into the engine bay

4. I put the fuse holder i the battery box - there's plenty of room even with the battery in.

