Nera Donna,
 
As Kev said, the USI-160 has a winch mode that hooks the two batteries together through a 160A solenoid.
 
See here for more details.
http://www.aulro.com/afvb/verandah/1...-isolator.html 
 
Tim was great! I was able to have a good chat and decide what was the best install, he gave me sound advice on the size of cable to run and all the heavy duty stuff arrived with lugs already soldered on.
 
Here is the kit after I had unpacked it.
https://www.aulro.com/afvb/images/im...11/09/1085.jpg
 
Tim makes the kits up to suit, so if you want some extra wire to run to the winch or to an Anderson plug to charge up the trailer, then he can make it up for you... 
 
As many have said before he is a legend and very willing to help.
 
Craig