Well, the first question I'd ask is, does your vehicle use the chassis/frame as the ground reference? If so, that makes your life a bit easier.
When calculating wiring sizes and lengths, not only do you need to take into account the maximum current, but also the voltage drop of the wiring.
The reason I asked about chassis/frame ground is that if you can do it that way, it essentially turns your negative/ground side return from your main power distribution bus into a huge fat pipe. The way it was explained to me is that electrons "like" to travel along the outer surface of your wire (I know it's cheesy but it's early, bear with me), therefor the more surface area of your conductive material you have, the less voltage drop there will be. Your vehicle's chassis/frame exposes a huge amount of surface area, and you really don't have to worry about length of wire due to routing.
So, with that out of the way, let's do a few rough calculations. We'll presume that you can use chassis/frame as a ground reference, and therefore the bulk of the high current cable you need to run is the V+ lead between your battery at the front of the vehicle and your main bus in the trunk, and conservatively estimate that it'll take about 20 feet of cable to do it.
Remember, because we're using chassis/frame as ground, this not totally but effectively eliminates non-trivial voltage drop from our calculations.
Here's the approximate resistance and voltage drop for a selection of wiring sizes:
0 AWG -> 0.0020 Ohms, 0.2v
1 AWG -> 0.0025 Ohms, 0.25v
2 AWG -> 0.0032 Ohms, 0.32v
I don't have the calculations for 1/0 AWG handy, but these should do.
So, under maximum theoretical load of 80A w/ 125% overhead, I'd say you could probably get away with 1 AWG. Presuming the vehicle is running, a 0.25v drop from 13.8v gives you about 13.55v, which should still easily be acceptable for your 12v applications.
Now, if you plan on running a lot of this equipment with the vehicle parked and not running, I would definitely encourage the addition of a second battery in the rear compartment, along with a battery isolation system. This is due more to the current draw than the voltage drop issue, although if you do do a secondary battery, you may be able to reduce the size of your wiring, since the equipment will draw off the aux battery and the V+ run from the primary battery/alternator would keep the back battery charged.
Regardless of which way you go about doing it, you'll want to make sure that your alternator is appropriately sized, not only to provide power to your equipment when the vehicle is running, but to be able to recharge one or both batteries after a period of sitting parked.
Your fuse ideas sound ok. I think I would increase the main bus fuse to at least 150A, and I would add a second one on the negative side of the bus, in the wiring from the negative bus to chassis/frame ground, and close to the bus itself.
Hopefully all this info will provide to be usefull. The calculations I used and also a very good article you may find usefull were obtained from this page:
http://www.stealth316.com/2-wire-resistance.htm
Also knowing what kind of vehicle this is may bring some input from those that have worked on them before, and some other suggestions.
Good luck with your project!
