I finally got around to installing a second battery on my F250 today. I thought that some of you might be interested here's some details and pics.

I bought an oem ford under body mount box (from an E series psd) I choose the inside of the drivers frame rail between the transfer case and fuel tank for the location, I used 2 x 1/4" flat stock and welded these 2 plates to the frame rail

pic 1

I then installed a standard 65 series battery (the same battery the truck takes) in this box

pic 2

Here's what it looks like all done

pic 3

I have all parts #'s used, if anyone needs for info let me know.