We came across the decision to relocate the battery when we put the electric water pump in. The pump would mount beneath the batter and it just seemed to be too big a deal to try to deal with all that stuff crammed into the front left corner of the engine bay. We chose the Moroso Battery relocation kit and a Flaming River cutoff switch. At the time, we had the electric water pump and a few other accessories that drew power which required us to develop a fusebox connection in the engine compartment.
We chose to run a ford F150 solenoid in the trunk and bypass the starter solenoid. This would enable us to not run a hot cable the lenght of the cabin full time. Some argue this deteriorates other systems as the F150 technology is old. I have not noticed a problem in nearly 4 years though I do keep a spare with me. If you look at the photograph we also attempted to put a fuse box in the hot line going forward to protect the car in the event of electrical issues down stream. The car was so violent on the dyno and street it threw the switch so we had to remove it. Was still a good idea.
To do this right you need to ground the car in the back, and you need to ground the engine in the front. For the cutoff to work, it has to break the power too or from the alternator. With a separate ground up front, the alternator continues to produce power even with the switch thrown. You have to link the alternator back through the cutoff switch for it to work.