rip the battery cabling out of an early BMW, its heavy guage, long enough to go to the boot (as BMW batteries are in the boot) and has a nice terminal block that you can use in the engine bay. the terminal block has 4 terminals on it and a point for jump starting (so you dont have to jump start in the boot)
my battery and washer bottle are in the boot, but the plan is to make a false floor in the boot, and move the battery etc away from its current home of the drivers side - if you can imagine most of the engine weight is on the drivers side. plus the driver sits on this side, plus sticking the battery on this side = fail!