The battery charger I have is an old Schumacher SC-600A. No clue where my old battery tender went

That was a thought as well, plug a small converter into an extension cord and run the fans off it. The trailer is used for storage/workshop (in a limited capacity) and for moves. Only time I'd really NEED to run the fans is once it's parked for an extended period of time. Would look into wiring to a switch and to the battery later down the road. Would just need to figure out how to stop power from going from converter to battery, just in case it gets parked and someone bumps the switch... But that can be dealt with later

I'll look into that, thanks!

And that's exactly what I'm trying to avoid... Damaging the battery

Unfortunately not... The sun here is still pretty low on the horizon and the trailer sits in the shadow of the house so it wouldn't do anything.

Your time is worth a lot more than nothing. Just because you offer it to them for free doesn't mean its worth nothing.