On the east side of town you have Sandy Riverfront RV Resort, and PortlandFairview RV park. Both are pretty decent. There is one just west of town, but I have heard it is in the airports flight path so can be really loud. There are two in Vancouver that are decent. From either of the two parks on the east side of town it is a short drive to Max,our light rail system where for a dollar you can get to town as a senior citizen. Much easier than driving and the best way to get down town. Although I don't understand why anyone would go down town except maybe to the court house. There is nothing there.
Be sure to bring an umbrella as June is still rain season.