Any heat gun will do the job if you intend to use it for heat straightening and belly tempering. Buy a heat gun that has two or three settings (easy to regulate the heat).
Apply heat first, and THEN back a bow. The heat will otherwise destroy the glue bond. It depends if a backing is required. But denim and paper make very lousy backings. Go for linen, silk or rawhide. And yes, TB3 will be fine for this.