I use a heat gun but always 3 feet away. First, I clip the front part on and just drape the whole top over the bows, rear bow still folded forward. Then I heat all areas of the surface as much as possible, then install the snaps, from the middle working outward toward the corners. I use the heat gun again in areas where it's uncooperative. When all the snaps are in, I heat the underside of the top from inside the car, then push the rear bow towards the seam above the rear window. Once that's in, I then heat the rear and quarter clear windows from the outside, evenly to smooth the wrinkles out. Long strokes.
You have to be careful, a hair dryer is probably safer. I have experience shrinking plastic covering on model airplanes so I'm confident in using the heat gun. It's very easy to burn a hole, if you're not cautious...
