My old trailer had two golf cart batts in a vented box inside. No problems.
I mounted the battery box with bolts through the side walls, not the bottom, so any battery leakage (and there definitely was some) collected on the bottom of the box and didn't drain into the trailer.
Later noticed that the side bolts were rubbing against the batteries, wearing into their walls, so added plastic spacers between the box walls and the batteries to prevent that.
With the new trailer, I thought about moving the batteries to a tray built on a reinforced rear bumper to reduce tongue weight like you. Electrically there wouldn't have been any problems, I think. The existing 6ga cable from the mid-trailer converter to the front junction box would feed the jack, stabilizers, and other (?) stuff.
But laziness got in the way, and now my Solar panel wiring is routed to a controller at the front near the batteries on the tongue. On the positive side, they say a high tongue weight makes for a more stable tow.;) But my truck doesn't particularly like it.:(