I saw a pic awhile back of someone who modified a milk crate to hold their deep cycle battery. I think it had a lid too, and it maybe served as an additional amount of storage space? I’d love to see some pictures if anybody has built one these and using it in their bass hunter / Pelican style boat.

The lid: take a second Crate and cut to keep the bottom. Common setup in kayak fishing world.

Mine doesn't have a lid...