[Where to put winch isolation switch?]

I use one of these

Seems reasonably priced, and allbright have a good reputation. The 180 is the continuous current rating, but for a few mins can pull much more. There are higher rated ones, but there is quite a jump in price. I have pulled some very stuck people out without it burning out. You could get a single warn winch solenoid, the type that make up the 4 pack of switches that run winches, and use on of those.

Did you need to seal it up? Aquired one of these and was scratching head about where to mount it, then noticed that the contacts are open to the air. Was worried that they could fill with mud and stuff and fail just when you need it.