Gmtech - I did the same you are are doing to the dash area on my Vegas a couple of years ago - also posted it , so you can search it. I added a layer of 1/8 mass loaded vinyl under all of tHe dash , also sealing all holes - of which there were many. Mass loaded vinyl , as used in recording studios ,etc - works great here, as you are going after airborn noise , not structure born like dynamat or the like attacks. Results were wonderful !
Keep after it - after a couple of years of re- engineering my Thor, it is becoming a pretty good motorhome !
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