3500 truck towing HT 5th wheel - Workable?

Dry weights of 8,000 lbs. to 9,000 lbs. are not real world weights. Go by the GVWR to get a decent idea of what the loaded weight will actually be. But those trailers would be in the neighborhood of 10,000 lb. loaded and around a 2,000 lb. hitch weight. So I certainly wouldn't see any issues with pulling/carrying it with your truck.

You don't say what year the truck is but if it's an older 3500 it shouldn't be an issue. A 3500 only a couple years old may have bed height concerns and be nose high.