Mounting battery under?

I am still in the frame building stage and about to buy a water tank that mounts under the belly of the camper and it got me to thinking. Since space is at a premium, why cant I mount the battery under the camper in the same fashion. I was thinking about putting it in one of those black plastic snap tight battery boxes then building a cage around it, that can be unbolted in some way (much like mounting a fuel cell in a race car). According to Walmart's website, the battery box is the same height as the water tank.--in thinking about ground clearance. Has anyone done this? Does anyone see any real draw backs? Thanks for the help.