I used several rolls of foil-backed asphaltish B-Quiet years ago in our '87 Westy and when that ran out I used cheaper and similar Peel & Stick roofing material from the hardware store.  Only had one piece come loose inside the driver's door and it gummed up the window but I cleaned that up and replaced it and have had no trouble since. I also took the precaution of taping all the seams with metal foil tape (not duct tape) to keep the gooey stuff away from surfaces I did not want gooed. 
Let me know if this photo link does not work for you:https://get.google.com/albumarchive/112729414255295600165/album/AF1QipPwCdrUOQZbNYvVI_rrJwRXplx7RnZaDa2J3CqK
Stephen 

    On Monday, October 31, 2016 12:38 PM, Dan N <dn92610@GMAIL.COM> wrote:
 

 the OEM firewall insulation is quite thick and I couldn't find it... so I
use the Fat Mat and double it