Good point. OP @2fpower must not have brakes on the trailer if he doesn't have the 7 pin connector. Might be a better idea, unless brakes are in future plans, to just separately add larger AWG wire through an Anderson connector to charge while on the road. I did that on mine in additition to a 7 pin connector. Also have a DVSR that will prevent draining the towing rig's batt if left connected without engine running for long period of time. Yeah, that means dealing with 2 connections to the trailer, but so what? The benefits are worth it.The largest wire that most 7 pin connectors can accept, on only some of the pins, is 10 ga. That's not big enough to do much even over a full day of driving. It's better than nothing, but not by a lot.
Here's some pics for reference: