How much does a dual battery kit cost over there? Will the 12,000 lb. Mile Marker be a good winch? Thanks. They are $525.00 at http://broncograveyard.com/products/cat/13/271/19107

I've seen the connection block and charging electronics (to prevent overcharging and allow auto switching between the two batteries for about $40-50. A separate box to put the battery in would probably run another $20-30. Plus, of course, the battery itself. There are lots of options for less than $100. There are a few very good standard batteries that are around $50-60. You don't have to buy a deep cycle battery, but it does make a lot of sense in this application.
I go with a major chain for batteries, because your chances of finding one if you have problems on a road trip go way up. Plus, your chances of pushing the problem to a store manager or higher are better, if they really try to jerk you around.

Finding the battery and tray over here is not a problem.

Knowing what other parts to buy and where to source them is kind of a problem.

Are parts necessary to build a dual battery system readily available stateside? Are they available in those big corporate stores?

The mile marker e9000 is really slow. Friend has one on a TJ. We have pulled pretty hard with it, just slower than my Warn x8000i. The cable is a lot thicker than mine. And I hate their controller. It is almost worth it for the price. I have seen warn M8000 around for $499.

If I ever get into mods to mine, I am thinking about going with this sort of Isolator http://www.hellroaring.com/4wheel.htm
They also show a winch diagram.

I don't know about quality, but I double-checked my ideas on an isolator with one of the maintenance supervisors at work. We were discussing something like this rather than a simple diode setup. I don't know about the quality of these units; I couldn't find the review when I followed their link, but their specs look good. I'd be curious to know if anyone else is familiar with their stuff. Thanks for throwing this out there and welcome to the board.