TLW has it right, Just take a couple of large plastic trash bags, some blue painter's tape and your vacuum. Wrap the bags around the foam, tape the overlap and area around hose (usually at side at zipper), apply vacuum and shrink the foam. Immediately after placement you should be able to tear the plastic bags off before complete expansion.
My wife has done this a few times and the process is awesome. When done, you will need to push, pull and slap the material into the proper position...
Good Luck!