Couple of thing to know for May long weekend in BC this year, Victoria Day long weekend is May 16, 17 &18 weekend:
BC Provincial parks will require a 3 night reservation for the long weekend. You can not book a reservation in a BC Provincial park for only 1 or 2 nights on a Stat weekend, This rule is for all BC Stat weekends only
Most if not all campgrounds will have opened by that weekend, unless it is still covered in snow.
Looks like Mount Fernie doesn't open until June 1 , that's what I get from the reservation calendar, most likely because of left over snow on the ground. There is contact info on the site you may want to check into.
Just about everyone in Canada on this first long weekend ( Victoria Day weekend) of the 2015 camping season will be out for the first time of the year, and I mean just about everyone. Campgrounds will be packed rain, shine or snow, which I have seen a couple of times on that long weekend.
However since your going to be in Fernie on the weekend of the 24th you won't have ant issues finding a place room at a open campground.
Soup