I am on a mission to try and reduce the road noise in our 09' Sprinter based RV.
In the cab :
#1) I bought several boxes of adhesive 3M Sound Reduction Matts : https://www.amazon.ca/3M-38500-19-11.../dp/B009XR48MM
and stuck them to the floor of the cab. Result : ...about 2 decibels of noise reduction
#2)undercoated the RV with Zeibart Rust proofing/sound deadening : Result : about another 2 decibels worth.
#3) bought a couple of sheets of Dynamat hood liner :
and applied a little bit to the small sections of exposed firewall and will apply more to the pass through storage directly behind the cab area in spring time. The Dynamat is extremely lightweight and very effective. If something like this would have been applied to the RV floor sandwich at the factory, we'd all be enjoying a QUIET ride.
At 55mph on the highway, I've gone from 78 decibels-A weighted to 72 decibels. By comparison, our Ford Edge measures 57 decibels !
No consideration is given at the RV factories that they've created a very large loud speaker box that resonates and amplifies road noise. The dually wheels alone create that typical, loud, whining highway truck noise. With no wheel well liners and only a thin sheet of plywood between them and your RV box...ugh...
For a vacation vehicle that we're supposed to enjoy on long trips, it's not as pleasant as it could be.