We have loved our stays at Haviland Lake national forest campground just north of Durango off 550 - all paved. There are a few electric sites but most are non-electric. It's in a beautiful setting. It's getting popular so you'll probably need reservations.
If you are towing a vehicle you might want to consider just driving it on your own up to Silverton. It's a neat frontier mining town to poke around at your leisure and you'd be able to drive any kind of vehicle to Animas Ghost Town which is a must.If you have a 4x4 you'll be able to do more roads up there. If you're taking the train you'll have only a short time in town, plus it's very expensive.
Another option is just driving your motorhome to Silverton from Durango. It's very doable and there are plenty of RV parks right in town.
From Silverton, I wouldn't advise driving the motorhome further north to Ouray unless you feel very comfortable on mountain roads. Many RVers do it, however, as we have done multiple times. If you want to get up to Ouray take 145 out of Cortez. It's a mountain drive, also, but easier than Red Mountain Hwy 550 from Silverton to Ouray.
Have a good trip!