I did this many, many years ago and the noise abated somewhat but it's purely subjective. I thought about doing it to the ceiling but there seems to be something up there already. According to a website that talks about the proper application of soundproofing material in a car, I used their 25% coverage rule. I'm sure it has helped but to what degree, I can't quantify. I do this to all of my vehicles.
both door panels
under seat
rear quarter panels
trunk - no
ceiling - no
I did find some petrified french fries and loose change in the process
