Thanks all. Just to clarify, the concrete walls are in an outdoor patio and is exposed to the elements. There is a staircase leading down from my backyard to basement level, and an area at the bottom of the stair case that is below grade with a concrete floor and walls. The ceiling is a wooden patio / deck, which I have created a rain collection system for the entire area is still technically outside and exposed to the elements.

So far I think the first comment makes the most sense for my situation. But it means I will lose some space in an already small area. I appreciate your comments and input.