You would also have lots of opportunities by taking I-15 south to Helena, where there are three major reservoirs on the Missouri River - Holter, Hauser, and Canyon Ferry. All three have designated campgrounds for you to set up shop. Each of these reservoirs has walleye and trout (rainbows and browns) along with perch and some lesser saught-after species. The Missouri River downstream of Holter Reservoir is world class for trout...very crowded too on any given summer evening. Lots of opportunites on Fort Peck in NE Montana too if you want to try that part of the world. Have fun and good luck!