I wanted a used 40' DP MH when I started looking. But when I test drove a few and rode in a few others there is NVH. Noise, Vibration, Harshness. I think a MH's rattle, shake, and roll down the road. Same inside the 5th wheel trailer...but not inside the truck cab.
The newer trucks are nice and quiet and smooth as Ford, Chevy & Ram have been working on making them that way.
When I am towing my 5th wheel with a 2012 diesel dually I pass all single rear axle MH's. The only MH's that pass me are tag axle MH's. So using this observation I am very very happy with the way my rig goes down the road. I have a mor-ryde pin box and mor-ryde suspension on the trailer. There is no chucking at all.
When I was looking a 5 year old DP cost more than a new 5th wheel and a new diesel dually.