That pvc coupling should work fine. Here's the shrinking tip on my dent puller. also referred to as a heating tip. It has enough mass that it doesn't "weld" like the normal tip, and will heat up a pin point area for a localized shrink.


https://hosting.photobucket.com/albums/y167/rmccartney/Metalworking/.highres/Picture207-1.jpg


Here's some shrinks:


https://hosting.photobucket.com/albums/y167/rmccartney/Metalworking/.highres/Picture208-1.jpg