Tonge box

I have been planning on building a tongue box on my trailer. I was a Lowes the other night & found this for $30. It is the exact size I was going to build. It is big enough to hold my 2 deep cycle batteries & room to spare.
Even though it is pretty rigid, I will build a frame out of angle iron to support it. I'm going to put a thin rubber seal around the top edge, add a couple small draw latches to the front & cut a slot in the front pocket for my power cutoff switch.
If I drill some drain hole in the bottom, do I need to vent it?

Even though it is pretty rigid, I will build a frame out of angle iron to support it. I'm going to put a thin rubber seal around the top edge, add a couple small draw latches to the front & cut a slot in the front pocket for my power cutoff switch.
If I drill some drain hole in the bottom, do I need to vent it?