Shrinkable plastic for a form?

[Verne_Frantz]

I've had no luck finding a source for a fairly heavy duty shrinkable plastic sheet. My intention is to heat shrink a sheet over an aluminum intake manifold (trim the edges) to use as a mask similar to what what was used at Tonawanda before painting an engine.
Plain overspray is not correct. A distinct edge can be seen in some places due to the mask used originally. Here's an example. Can anyone help with a source for the product I need?
Thanks
Verne [img]<<GRAEMLIN_URL>>/biggthumpup.gif[/img]