Most recently, I've been applying Kilmat to the front doors and rear wall of the cab. While in the front doors, I replaced the stock speakers with some Rockford Fosgates. Still need to do the rear doors and replace those speakers when the weather cooperates.
Front door stripped with speaker out, then a bit of Kilmat on inside of door. (I have pictures of completed door somewhere, I need to track them down and I'll add.)
With the front doors completely covered, there is definitely a satisfying "thunk" when you close those doors now, rather than the hallow sound before the Kilmat.