Missoula is a great town with some good fishing. I usually travel the 200 miles to Missoula in late March to chase some of the first dry fly fishing with flies larger than a # 18 midge. There should be a few Skwala's starting to hatch around the time you are looking to be out here and it only takes a few bugs to get the fish interested in looking upward towards the surface. Depending on the dates you may also see some BWO's as well. I usually head over a bit early, St. Patrick's day, and have had decent dry fly fishing with only a few bugs out. Good luck with your trip, where ever you end up.