Do not let the cover sit on the cooker and do not cover it to the ground. You are creating the conditions for condensation by covering it completely. You need to get air to circulate around the grill while it is covered.
Of course, a shed is a nicer answer
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."