For just an overnight in Prince George there is the Casino lot at the Hwy16/97 intersection. Walmart on hwy 16 west. There are three commercial RV grounds just south of PG. Blue Cedar rv on 16 west. A short distance west of Walmart there is an ESSO that has all the fuels, propane and free dump.
RV park in the village of Hixon. Between Hixon and Quesnel a one store place called Cinema with an antique store with free rv parking.
West of PG there are many great places. In Telkwa there is Fort Telkwa RV park but haven't been there for a few years.
If you have the time I highly recommend Stewart/Hyder to see the grizzles catching the salmon. Bring your passports for that.
This website for great information on where you are traveling, http://suethomas.ca/