I should start by saying that I referenced GeoXplorer's dual battery how-to thread quite a bit, it really helped me figure things out.
I broke my installation down into 2 major steps, 1; moving the power steering reservoir, and 2; installing the dual batteries. (I separated the 2nd step into two "sub-categories", 1; the battery tray fabrication and moving around of stuff to physically fit the batteries, and 2; the wiring.
I worked on this project over a month. Getting the PSR moved first, then sitting down and trying to sort out the rest in my head before tackling the remainder. I decided to use a new pair of Deka Intimidator AGM batteries. They seem to get good reviews, and I got a good deal on them from our battery supplier at work.
Moving the power steering reservoir, not that difficult a project. I just went to GeoXplorer's how-to and pretty much followed that. I had to space my transmission dipstick out a tad so that my new PSR bracket would fit and still allow me to check the tranny fluid, and fabrication my own new PSR bracket hold down with some metal I had kicking around. I found hi-temperature hose in both required sizes at my local NAPA.
Next step, fabbing up the battery trays, and moving (coaxing) some other things around to get the room required for the pair of Deka's.
I unscrewed the one leg screw on the smaller fuse box, pushed it back a bit, and re-screwed it in, to gain some space. I did the same with the lower coolant reservoir bottle screw. I bent the front battery hold down bracket over to make space, and completely cut the one metal raised up section out of the way (the raised piece that the PSR was originally attached to). I fabbed up a bracket for the front tie down bolt, and drilled a new hole in the rear section for the rear tie down bolt. I tried to be aware of any wiring harness that may be too close to the new battery trays and did my best to re-route them and/or secure them out of the way. I secured the new battery tray to the body with screws, and as the tie down bolts are attached through the body as well it should all hold in place.
Once the batteries were stuffed into the trays, I made a stepped hold down bracket from and old shelving bracket and bolted them down. They are in their tight, easily as secured as the stock setup.
Then I got onto the wiring. I had installed the T-Max control box into the vehicle a month ago, when I was running wiring for my new lights, and a wiring harness for me new Dometic fridge.
The instructions that come with the T-Max control unit are simple enough, but the diagram is very small and hard to see. I referenced better large diagrams online in order to double check what I was doing.
I extended the negative cable from the block and frame to gain some room to maneuver and ran a second negative cable from the same spot to my aux. battery. I mounted the T-Max solenoid on the firewall and ran one control wire to it, one negative control wire to the main battery, and the two large positive cables from it to the batteries. (The instructions call for running two other control wires directly to the positive posts on each battery, but I simply ran them to the corresponding posts on the solenoid instead. Same difference.)
I cleaned up the wiring as much as possible. I have run the winch to the main battery, and all other accessories will run to the auxiliary ( fridge power and driving lights for now).
I will (at some point) invest in a decent fuse block to try to clean things up a little more, but for now it all functions. The batteries are clear of any moving parts, even though they are really jammed in there. Their is also ample clearance under the hood ( I sandwiched some foam between the batteries and hood to see if their was any deep impressions in the foam...and it's all good)
I just went at it very slow and methodical, with help from members here, and measuring and re-measuring before any final install. I am fortunate enough that the Xterra is not my daily driver (or Wife's anymore) so that allowed me to be able to not rush things.
I really tried to think things out before making any "point of no return" type modifications. The project was a little intimidating for me, but I just took my time and thought everything out before committing.
Having some issues with Photobucket all of a sudden, I'll have to add the missing pictures here.