As stated they are a truck and they will ride harshly and rattle especially when they are empty.When loaded with your camping gear and everything else the chassis will be loaded and smooth out the ride and lessen the noise.
In my search for a Class C all I drove were on a Ford Chassis and noise from the engine and rough ride seemed common,then I drove one on a
Chevy Chassis and the noise and harshness of the ride was remarkably different.Soother,quieter and easier to drive.
So maybe try to find one on a Chevy Chassis and give it try