Great idea, I think there's definately a market for anything 1/2 sorted when it comes to electrical..
Taking it the next step beyond just an updated fuse holder, with relays and proper fuse protection would be a goer, especially if it gives you the backbone to use whats left of the wiring (like the cluster,brake fail etc).
We have been debating the likely issues of having the van battery inside behind the drivers seat when it comes to RWC.
I had planned to have the positive feed go over the gearbox hump, down the passenger floor, and exit the firewall, lining up with the starter motor. Then take a feed (or 2 actually) from the back of the starter motor, back to the new fuseblock, in its std location.
My gold rally pack had basically this setup, with battery in the boot, live through the cabin, and feed from the starter. It might be thats how its done, but it seemed pretty not having to go all the way back to the battery for power. Battrey box would have a disconnect switch, an a charger pigtail parmanently connected.Probably should have a main fuse in there somewhere.
Fingers crossed, I hope to be getting the soldering iron out pretty soon, so it can get started up,otherwise i'd wait to see what you come up with. So any thoughts or comments on how people have done it, would be great.