Here is an early picture of mine. Just one load when I took this so only one fuse. I did something a little fancy, if you look close you can see two larger wires coming out of the top of the block. One goes to each battery, primary and secondary. The batteries are isolated, the primary is the stock truck battery, secondary is the one I added. I cut out the notches in the fuse block a little bit so I could move the fuses up and down one hole. The top row is a buss from the primary battery, the second row are 4 individual loads, the third row is a buss from the secondary battery. Then the next three rows repeat and the next three repeat again so I can have a total of 12 loads and each can be individually selected to be powered by the primary or secondary battery simply by moving the fuse up or down one position. If one battery should fail I can simply move anything I need/want over to the other. I have a degree in electronic engineering so I tend to over engineer 
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