How to prevent mold from growing under stand?

[Palster]

I have a 90 gallon tank with a sump underneath it. The tank came complete with the sump and a stand made out of 1 inch square tubing. I wanted to close the stand in for aesthetic reasons so I welded some tabs onto the 1 inch tubing and closed the stand in with stained good one side plywood. The end product looks pretty good but the problem I am having is moisture from the sump is causing mold to grow on the plywood inside the stand. Does anybody have any ideas on how to prevent this from happening? I am even considering replacing the plywood on the front of the stand with something else that would allow the moisture to exit the stand or maybe some vent holes would be in order.