My trailer stays plugged in at home from the first trip of the season to the last. It's plugged into a regular outlet in the shed by my driveway. I just use a 20 foot extension cord and an adapter.
I keep my refrigerator on auto all season so that when I unplug to go camping it switches over to propane for the road. Makes for a lot less packing since there is always stuff in the fridge and when I shop for a trip, the cold stuff goes right from the truck to the camper without ever going inside the house :-)
Ray