Like metalmaker said, bedliner lasts well, I painted in my Jeeps wheel wells 3 years ago and they look like new.
I'm going to use almost a gallon of bedliner on my 818, this includes painting almost all aluminum and all of the backside of all the fiberglass panels. I can't imagine that a gallon even weighs 10 lbs and probably 25% is the carrier that will evaporate.
Not sure what the acoustic benefit will be, but it will will be some, and at least better than just black paint that would still be needed to make the wheel wells look good.