After the fact I did not like the that you could see thru the speaker grill so I ended up buying some black felt like material and hot glued it to the back side so you really can't see thru anymore.
For what it's worth, my truck was originally speakerless, being a plain-jane fleet truck, and had a piece of heavy black paper behind the grille. I had some black construction paper on hand so used that behind the grille before reinstalling it.
You did good with the black felt.
