In that stretch of the Alaska Highway between Grande Prairie and Ft. Nelson, you don't have to go all the way to Liard Hot Springs to find a campsite. Several little towns between Grande Prairie and Dawson Creek have public campgrounds with hookups, like Sunset Park in Wembley, Pioneer Campground in Beaverlodge, and Hommy County Park between Beaverlodge and Hythe. Try the no-reservation city park campground in tiny Hythe, AB--electric and water hookups with dump, flush toilets, and showers for a very reasonable rate. There is also the no-hookup Demmitt Provincial Park a couple of miles east of the AB-BC border.
North of Ft. Nelson, there are several good parks many miles before Liard Hot Springs. The private Tetsa River Services campground (75 miles north of Ft. Nelson) and the scenic, well-maintained, well-run private RV park at Toad River (good WiFi too) are worth making a reservation to stay in, if necessary. There is also the Tetsa River Regional Park about 15 miles east of Tetsa River Services, which, again, has no hookups. You can fill up with water and use a free dump at the old visitor center in Ft. Nelson (across the highway from the new visitor center).
But, based on our experience and that of others, do not be tempted to call it a day at the RV parks at either Pink Mtn. or Sikanni River. They are full of long-term oilfield workers, which means you get the expensive, muddy, poorly maintained, leftover sites.