Your trailer 12VDC Parasitic Drains will run your truck start battery down just as easy as it will run down your trailer battery. Not a good idea to me.
I would install 120VAC to your "trailer barn" and plug the trailer shore power cable into an installed RV 30AMP pedestal type receptacle or at least into the 120VAC Receptacle using a RV30A-15A long 'dogbone' type adapter (WALMART). This will run your trailer on-board converter/charger unit to keep your trailer batteries charged up.
Rule number one in my book is never mess with the truck 12VDC start battery system as the truck is the only way you can get back home with...
Roy Ken
