Defroster and dynamat

Ok in my car I'm having some rattle issues from the b-post panels I think is what they are called. (The plastic panels that run from roof to rear deck that makes contact with the rear window). I'm looking to dynamat them so they don't rattle(Mainly at the very base since the defroster component sticking on both sides keeps like the top 70% gapped enough for no rattle.) Now I've got an idea of how I wanna do it so when the rear deck is slid in it will all snug up and get comfy, I was just wondering how the defroster will affect the dynamat material (Xtreme Dynamat). Will this create a messy problem or will the defroster have to get unimagineably hot before it gets affected? It won't be directly touching any of the window cross lines, just the black areas on the outside at the bottom. I live in Southwestern ohio, we have our "too cold to go without it so don't even try" days and I am not entirely sure how warm the window gets (Never thought to feel).

Also, when I hear the rattle, I can locate all of I think, but it sounds like maybe there is something behind these panels that could be rattling, and I'm not entirely sure how to get them off of there right now. Anyone know if there is something of concern? I'd prefer to not have to take all the backseat and rear deck out again (Top mounted speakers that are exposed over the rear deck carpetting) to get back there later. Thank you!