Campgrounds - There are several nice ones, I'm sure someone will have suggestions. We stayed at the National Forest Service CG above Durango: not bad if you don't want hookups (has electric only) and don't mind 2 miles of washboard roads to get there. I'll stay in one of the ones in town next time.
Train - Great ride. Reserve ahead and try to get an open car if you want to take pix. Cooler too, but take sunglasses so you won't get embers in your eyes. I prefer the right side going up (leaving Durango). Also take a walk through the train museum.