Large plastic sheets are available online from many suppliers. Check out the United States Plastic Corp. for material, or be creative and use things ...
Step 9: Done with Molding
The plastic will suck tight to the object and the workspace. If when you turn off the vacuum cleaner, the plastic is still gooey enough to try to come up slightly, hit it again with another burst from the vacuum cleaner. It should be done by that point. Hold it steady as the plastic totally hardens. When it is done, leave it alone for a little while so the plastic can cool off.
Once the plastic is cooled, take the frames off the plastic. It should look something like this: