They (Idaho state) has a really neat book they send out (atleast couple of years ago) that has all there neat stuff. And see
http://www.visitidaho.org/This last trip over there (family business) found a neat RV park in back of Costco in Clarkston WA (about 5 blocks from Idaho) with all the store to re-supply and right along river. Perfect for Lewiston/ Clarkston to get caught up on wash, mail etc before hitting boonies. Google maps has name as Premier RV resort at L&L of 46.424088,-117.044224.
http://www.premierrvresorts.com/PRVR/(S(etsqte55o4hqa120cwzfgl45))/Pages/p0130LocationDetails.aspx Not cheap but everything is maybe a 5 min walk right on river. Did stay just noticed when taking Mom in law shopping at Costco.