I cut a piece of 3/8" plywood the size of the battery and painted it real well, put some 1" X 2" wood strips on both sides to hold it up from contacting the battery posts and allow air to circulate and mounted it to the top of the battery on the drivers side, using longer battery hold down bolts.
Put all wires in a split loom large enough to add to if necessary, then put a service loop in the loom long enough to allow the whole plate to be removed to allow easy servicing of the battery.
I have both key on and hot all the time circuits on the board, including a 75 amp relay for the inverter that powers a computer.
Makes a clean neat set up and with all the 06 alarms that go off when you add anything, it is a lot simpler to do it this way. I found out when I installed useable backup lights and the horn sounded and the four ways flashed telling me I screwed up.
Denny