Here is how I soundproofed the "new" bus. I ordered up 160 square feet (80 1' x 2' panels) of Damplifier from Second Skin. It is sort of a thick (~3mm) aluminum foil over a butyl membrane and sticks pretty good on a clean surface.
Here is what I started with....
It cleaned up pretty good with some "scubbing bubbles" and a good rinse....
The Damplifier has a paper backer that peels off and sort of looks like this....
I used full sheets whenever I could and you have to measure sometimes as you install...
They stick pretty good and then you use a small J roller to get good contact with the surface and roll out the air bubbles. Sometimes you have to slice it with a utility knife to get all of the air out that you can. The foil is sharp and I did manage to cut myself until I smartened up and used some gloves.
Here is sort of what it looked like when I was done. The plan was to cover about all of the inerior painted surfaces that would not show when the interior is re-installed. I went double layers over the engine compartment and under the rear seat. I used the small leftover pieces to do the spare tire well, most of the driver and passenger seats, and around the pedals.
More a little later....