If I had a new pontoon boat, I would first try a shorter drift, like Lydl bridge to Stinson, or Klickitat to Pitt bridge. You have a great advantage over driftboat floks because you can put in and take out almost anywhere. You could start at the campground at MP5, and drive upstream checking out places to launch and take out. Manytimes there is a "wide spot" informal parking lot along the river that can accomodate 2-3 rigs. Most of the river is class I-II but beware of sweepers and scout blind turns.