If you are a confident trailer puller I'm sure some of the sites around the lake are tight but doable. All these spots you can see right into your neighbors spots, not quite as private as Castle Falls campground or Castle River bridge. All spots here are right close to water. All sites have brush in between so quite private. I would think midweek you should have your pick of sites.
Visit
http://rockymountaincamping.ca/
This has all the local campgrounds as well as site sizes for your trailer.