Fred,
Yes you can. Once you hook it up to the trailer, make sure that one of the wire is a direct 12 volt feed, as when the trailer is hooked up to the tow rig, it will charge the battery. When it's disconnect it looses charge.
The 7 pin connectors have an extra/aux wire for 12 volt feed, for when it hooked up to the tow rig. Just make sure you use a heavier gauge wire for the Aux feed.
Rob