Got the interior all put together this morning and took it for a test drive with MsBoyink.
I ran a dB meter before starting the sound deadening and ran it again today. It's tough to be too scientific about it - sound level is affected by wind, road type, tire noise, etc so the level is always jumping around. And dB is a logarithmic scale so it's tough to map the numbers you see to what you are experiencing.
But - pre sound deadening the dB's pretty well matched our speed - 75db at 75 MPH, etc. This time the sound level seemed to stay the same (low 70's) from 55 MPH up to 80.
Experientially, it's much improved. MsBoyink didn't have her hearing aid in, I had the stereo playing loud enough to hear it well, and we could still have a normal conversation.
So, worth it, yes.
But man, that was laborious.
I do note the material cost went up - my first order was $55/box. It's now $70. I used 7 boxes total, 140 sq ft, and about 100lbs altogether.