Used a WEPR kit in the past but if I were doing it again I'd use a sealed battery box to keep things safe (and sprint regulation friendly). Would be a good idea to stick a fuse in the set up just in case something goes wrong. I fed a thick gauge positive through the bulkhead, into the passenger foot well and through the rear of the car to the battery. Other end was bolted to the main positive terminal on the wiring loom. The earth was just earthed to the boot floor for handiness.