A year or so ago, I put a OD Canvas battery box cover with foam padding in my truck. I just redid the design a little to get it to stay on the box better. Next step is to add a couple of cup-holders. I used closed-cell foam so that it doesn't absorb water when it gets wet.

The padded cover makes driving around a lot more comfortable especially offroad since you don't bash you elbow on the steel box.