Water in UDS

After every use and cool down I empty ashes, close all valves, replace lid, and cover with a grill cover. While the grill cover does not cover to the ground it does go about half way. However, every time I use it there is approximately a quarter cup of water accumulated in the bottom which I empty out.

Curious if others experience the same and possible cause. I live in a humid area and think it may be condensation.

Any thoughts?