Is a Battery isolator necessary

[alex2929]

I have a 2015 Sierra 2500 with a duramax.  I bought an enclosed trailer.  I am adding additional interior lights, a radio, and battery inside the trailer.   I know the truck will charge the battery inside the trailer through the 7-pin trailer connection.  If I am inside the trailer with lights on, etc is their anything on the truck to protect the batteries from drawing them down?   Or do I need to incorporate an isolator to protect it.  It is a snowmobile trailer so the last thing I want is half dead batteries when it is cold out.  

[revrnd]

If I'm parked for any length of time with my trailer hooked up, I unplug the trailer. I learned my lesson several years ago. Hooked up my popup trailer the night before departure & in the morning the battery was dead. The fridge had killed it.

Not sure how you would isolate a trailer battery though. I had dual batteries on a truck in the 80s w/ an isolator to power the winch.