I have completed an install of one of the military Warn 18,000 lb electric winches, and I got got such a great deal on the winch itself I bought an extra thinking I could mount it to the rear. I am thinking of creating something to span the frame channels but before I start trying to reinvent something I thought I would see if anyone has had success. I searched and found some threads on the rear PTO or self contained gas units but nothing I could really look at applying to this electric unit. Here is a picture of the one I mounted on the front. 
