I have a Tiffin on a FRED. What everyone is saying for the most part is true. Louder than a rear engine. But, not too loud. I just pulled everything apart and reinsulated and sound proofed the engine bay. Made a huge difference.
Leaf springs, not air suspension. So, the ride is rougher. But, Koni shocks help.
Mileage is great. I can get 9 mpg towing a trailer.
It is a compromise. Slightly better than a Ford V-10. Not as nice as a DP. Perfect for what we were looking for.
My next rig will be a DP.
Good luck. Ask me any questions you want.