Yes, you're correct - it will make a difference. If you want to make a REAL difference in sound quality, you should seriously consider dynamat ( or other equivalent material) in the doors, side panels and floor. It's a lot more hassle to prep but IMO, you only do it once and it's well worth the effort.
FWIW, I installed a mounting board on top of the dynamat behind the rear seats in my Quadcab and this then provides an excellent platform for mounting all the goodies :-laf.
I see from your sig file you're well on the way to ICE-bomb status. You might want to run a search in the TDR forums ont his topic - there was a thread a few months back about a very knowledgable TDR member who fabricated some kick panels with integral speakers in the footwell, rather than use the factory door positions. Good luck with your own plans!!