I'm projecting a need of about 25,000 bu........so about 4ft high, 50ft wide.  Your numbers indicate that I should be able to get real close by going just a bit wider, and avoid putting a lot of pressure against the outside.

The plastic and vac would solve the dirt problem.

If I can get away without pounding posts into the ground.........would rather do that.......although sometimes I think a permanent bumper around the inside of that bldg would be a good hedge against somebody falling asleep while parking machinery.......since they seem to think that leaving any distance between wall and other machinery is against the laws of Nature.

Do the neighbors or you put any ventilation thru the pile?