There are numerous spots at Liard that fit our truck and fifth wheel, with a 43' total length. It's a nice spot to overnight.
The open area across the highway is available at no cost. I'm not a fan of it though because it is dirty (large garbage bins there and the garbage tends to get scattered all over). As well, it is used by semi trucks stopping for a break so it can be busy. Whereas the campground is peaceful, clean and you get your own space.
In Watson Lake your choice is limited...the Downtown RV Park is likely where you'll end up. It isn't much more than a gravel parking lot with posts for services, and for Wi-Fi you need to be very close to the office or go sit by the office. This park is close to the grocery store, just a block away, so easy to walk. Wye Lake Park is just up the road too, with many hiking trails and good birding if you're into that.