My sister's 2020 Forester only has two rattle sources: The stove cover, and the ladder storage hooks. The stove was solved with a dish towel. Otherwise, it surprisingly quiet. Except on bad gravel washboards. Then everything shakes and makes noise. Most of it is probably pots/pans/furnishings etc and not the coach itself.
There's huge differences in construction methods, and fit & finish, which surely makes a big difference.
Also, do you know for sure the body was original to your chassis? For a long time, Cruise America used to swap old bodies onto new chassis. Until they finally realized the chassis is the longest lasting component. But I think they did this though the mid-2000's.
2000 Ford E450 V10 VAN! 450,000+ miles
2014 ORV really big trailer
2015 Ford Focus ST