Same here. Installed mine over my sunscreen. The magnetic sides hold nicely. Definitely a difference in nouse and heat. I think it cuts down on the crosswind. Seems to be a little more comfortable for the kids.
So I installed mine today. I did exactly the same as mentioned in this thread. I used killmat, kicker CS 6.5s and some filler. Very easy to install, and I hear a difference. Especially in the bass. Alot more happening in the back seat. Happy with the upgrade.
Note. Grills sit every flat...