dual batteries
You can adapt the battery try by removing it and extending the side straps out. Cut them off and weld an strap to move each out about 1". That makes it where you can get 2 batteries in the tray. You can get by using the same mounting bolts at the top. Or you can extend those straps, but I didn't. Need to put a spacer in the bottom so the battery isn't sitting on the sharp sides of the tray.
As far as the isolation, I prefer installing a 2nd alternator in the place of the A/C compressor. That is, presuming you don't have A/C. You can get a typical Motorcraft alternator and make a bracket out of 2 pieces of angle iron across the bottom that extend up to hold the alternator. Just have to cut a good sized notch in the angle irons to hold the alternator. They have a built in regulator so are easy to install and wire.
The standard serpentine for A/C should fit. I don't remember just which one I used. You need to make a 1" strap to wrap up over the fins on the alternator to keep them from hitting the upper radiator hose. Just take a 1" strap, form it in a semi-circle and twist each end 90 degrees to bolt to the alternator.
You can put a continuous duty solenoid between the batteries with a momentary contact. That allows you to parallel them if needed or to use the spare battery to starting if the main one is dead. Just be sure to pull power for the solenoid from the spare battery.
With the 2nd battery for winching, if you do kill the battery completely you won't kill the main vehicle and it will still start.