By far the best method to heat shrink window film for the rear window is the "Mdog soap shrink" method.
It works very similarly to the Dryer sheet method, but since dryer sheets are very toxic, the soap method should be used instead.
Very simply, the soap method allows the film to hover over the glass while heat shrinking until it is ready to lay down, then when the film is smoothed, it will lay down on the glass, while still allowing movement over the glass without binding and sticking which can cause creasing.
First clean the out side of the rear window with any glass cleaner or soapy water. Next lather up a paper shop towel or a micro fiber towel by spraying the towel with water and rubbing it with ordinary bar soap. Most any soap will work, but we recommend Ivory bar soap.
Wipe the lathered towel all over the window until it leaves a thin film of soap. It will dry very quickly.
You can make a damp H shaped area for your anchor or just leave it dry, the tint will stick to your anchor either way.
Once the soap film is completely dry, lay your widow film over the window.
Anchor it to the glass by using a hard card to make a horizontal line about 3 inches wide.
Trim the film oversize to allow for shrinkage and any edge melt.
Begin shrinking the film as you normally would, near the anchor. As you see the film begin to shrink, smooth it down with your gloved hand or a rolled up shop towel. It will lay down nicely, but still allow side to side movement while you shrink other areas. Continue until you get to the top and bottom edges.
As always, move excess film from the left and right sides to the top and bottom before shrinking.
Once all the film is shrunk, force a few fingers of film to pop up by pushing sideways at the edge, then shrink those fingers to ensure you have a complete shrink so that you don't have any fingers popping up during installation.
Trim film to size and install. Good luck!