I found some 3mil 55 gallon bags at Menards.  They're still too small.  I want to store some displays that are 4' wide and about 6" thick.  Some of them are 4'x4' approximately and others are maybe 4'x6'.  I could use a bag over each end and tape them together for the long ones.  

I have to seal them up because of where I'm storing them, they have to be kept clean and free of mouse or raccoon droppings.