I haven't done it, but how about on top of the tongue box, if its sturdy enough, and then moving the door from the top of the box to a side, which still allow access? Or, a larger battery box with the battery on the tongue, and the tongue box on top of that? A project, yes, but otherwise you are correct. I don't see any room on the tongue for a battery.
The only place I can see to expand is upward, unless you move the propane tank. How about moving the propane tank to the top of the box, thus creating room for the battery?
Or, attaching the propane tank to the front of the trailer with some kind of home-built contraption, again creating a place for a heavy battery on the tongue? Yeah, upon further review, that's the idea I'd explore first. Easier transition, separates sparks from gas, and no change to the tongue box.
I suppose a very good welder with some engineering background could fashion a box attached to the side of the trailer tongue somewhere, but it would have to be mighty sturdy to support the weight of a battery over pot holes, rough roads, wash boards, etc. Might affect turning radius too.
I bet some creative mind on here will have an idea though! (I'm just a copycat anyway!)
Definitely keep us posted!
