Just catching up on my reading here, and thought I'd chime in on the battery question. I use a lot of Optimas (4 trucks, two with dual battery setups). I had one Optima red die while in warranty, and another got fried by a malfunctioning high output alternator in my Z71. The battery dealer I use told me that they have had a lot of trouble with Optima compared to Odyssey, and strongly recommended that I switch to Odyssey when I replace batteries. Problem is, none of my current Optimas will die. But I will go to Odyssey when I have to replace one.
The dual battery in my PW is mounted in an open steel box, bolted under the cab outboard of the right frame rail, with welding cable routed through the frame channel into the engine compartment. Switching is via the Painless Performance high-amp waterproof isolator/solenoid. The battery box is bolted to the frame rail, battery on its side for easy access, and the box was built up from a race box sold by Summit. I reinforced the box with an angle iron frame and gussetted brackets, and nothing hangs down below the frame. No electrical problems in wet mud or mild water crossings, and the box is strong enough with the reinforcements that if I break it off I'll have bigger problems than just the battery. Box holds an Optima now, but will also take an Odyssey later.
Aside from winching and lights and radios, one good thing about the second battery is that when my Z71 alternator crapped out, I was able to drive almost 100 miles through the desert just on the batteries (two Optimas, one red, one yellow). Got me back to civilization.