3 site's come to mind in the BC interior...
Noisey creek FS Campground
approx 25km of gravel and one steeep hill climb down to the shoreline of mable lake but one of the nicest mid-week camp sites on mable lake you will wake up to unmolested views of wild shoreline as far as your eye can see with some awsome sport fishing, no hookup's and i wouldent drag anything more then 26' long there but have seen 36'+ 5th wheels down there.
Frog Fall's FS Campground
approx 5km south of 3 valley gap hotel turn down the "wap lake FSR" 5km you will see the sign, very private site with little to no use year round backing onto a beautiful creek with a large waterfall approx 20min hike upstream. no trailers over 20' will make it into the campground but lot's of parking at the entrance of the site for larger unit's.
BC Park's maintained site, load's of info online about it... located approx 30min from Salmonarm on the back side of Shuswap Lake easily accesable by the biggest trailers and i believe they have hookup's on site... Margret Fall's are a nice 20min hike from the campground's and the water there is about the cleanest you will find for swimming on shuswap lake.
I live in Kelowna and know a massive area of the north Shuswap and travel it on a regular basis so if anyone wants info on out of the way spot's drop me a PM