It seems a lot of folks already have a dual battery setup, but I though I'd show how mine is done. Thanks to Ed Cooke who used to work at 4x4 Connection for assisting in the design.

The primary battery is wired normally to the isolator, but the secondary runs through a circuit breaker to the isolator. An FJ-40 fuse block is in parallel with the secondary connections to provide power for accessories.

You will also have to relocate the coolant overflow tank. There appears to be a mounting bracket for it already on the fender.

Figure 1 is a schematic of the setup. Figure 2,1 shows the fuse block in the 'Cruiser. Figure 2,2 shows the location of the coolant tank.