You should have heard my F350 scream in the Rockies. It's the nature of the beast when you're sitting over the engine. You can only quiet it so much. People insulate the dog house, but neglect everything under their feet.
You might want to look into Acoustic/blok for floor area in addition to insulating the dog house. I have to say that Ford has incorporated some of the after market ideas into their newest chassis, like large front trak bar.
My drives well and has nearly no movement from large trucks, but I'm still going to add a Safe-t-plus just for safety. Does you coach go straight on flat roads with nothing else affecting it?