After cutting your panel to size, run the foam tape on the back side of your panel. The foam will fill the gap between the door shell and your trim panel. Also, in using the ABS plastic instead of wood, the plastic is strong enough to keep from breaking, is as light or lighter than the wood, and is weather resistant if the back side gets wet for some reason.

3M has a product called dual lock. This is extremely close, if not indentical to velcro. RodDoors recommends using roughly 10-15 1" square pieces to hold the trim panel to the door. This makes sense on a lot of levels, as you don't have to worry about the panel coming loose, makes removing and reinstalling the trim extremely easy in case of servicing anything in the door.

Set four pieces of Dual Lock in the four corners of your door. Make sure you allow about a 1/2" to 3/4" (give or take) to allow for the foam edging. Pull the tab off the Dual Lock and press the oversized panel against the door shell. Mark the trim panel against the door shell. Pull the panel off the door and cut along the scribed line. Run the foam tap along the edge of the panel with the edge of the tape hanging over the edge of the trim panel. It's easier to trim the tape to the edge than run the tape straight.

As most of the material is roughly 1/8" think as it wraps around the panel, take a sanding block and sand an 1/8" off the panel (and eliminate the rough edge) and the tape will be sanded at the same time to conform to the panel. All they used to attach the material to the abs plastic is spray clue. Even when wrapped around the panel, the material was simply glued.

RodDoors has prefabed flame style trim panels (amoungst others). The how-to video is $29 (I found my catalog).