Repairing cracked interior panel?
 

I was replacing the sub in my Tahoe over the weekend and managed to put ~18" crack in the rear pillar panel. Has anyone used a better method to repair these plastic panels other than just slathering on a bunch of plastic weld epoxy on the back side of the panel? This particular panel has a lot of the foam sound deadening material glued on the back side where the crack is and I can't get to the base of the crack thru the crack itself without elongating the crack more.
Also, does anyone know what type of plastic the interior panels are made of? I would assume ABS but didn't know for certain. Some of the plastic repair/adhesion products I have looked up do not work with some poly plastics.

I cracked a trim piece in a friends car installing rear speakers. Used a soldering iron and scribed the back of the panel keeping to keep them together and about a dime size of jb weld over the crack (back side). Can't tell there's a crack in it even running your hand over it.

I tried your method and it worked out pretty well. I scored the back side of the crack with a soldering iron, lightly sanded the area over and around the crack, cleaned with acetone then slathered on a good bit of plastic weld epoxy for extra rigidity. I can still see portions of the crack but it is not a glaring flaw in the panel. Thanks for the incite.
FYI to anyone else, the foam sound deadening is not glued to the panel as I originally thought but rather just held in place with three metal clips.