A tight seal requires full coverage on both walls and across the top of the pile. The sides and top must be placed so that there is generous overlap between the layers so that they can be weighed down for a good seal.
Use weighted objects like gravel bags, tire sidewalls, heavy sheet materials, etc. to ensure complete contact between the cover and the ensiled materials. Discrete weights like gravel bags should be lain with no gaps, and the weights should be as heavy as possible to help maintain the density of the material.
