I just got done doing both.. I went w/ "roadkill" I put in on everything, and taped the hell out of all joints (I heard about the leakage talked about above)
and ordered a carpet kit from Tuckers. I think there is a big difference from before. a lot less rattle, and less road noise.
a few tips:
WEAR GLOVES my hands look like they went through a shredder, someone on here gave me the same tip... I should have listened!
get a good aluminum tape.
if your carpet has a pad glues on the back it was much easier to cut it off, glue it down to the floor of my truck where it went then gluse the carpet down over it. it was not working trying to glue them both down together.
my carpet only had pad around the trans area. I added more pad to cover the whole floor.
maybe 6 hours total, with the help of my 2 year old... (pass dad the tape!)
let us know what you deside and how it goes.
also lay the carpet out in the sun for a few hours...