I am a huge fan of the WSM.. I am either using it or my custom wood burner. Most of the others just get left out in the cold these days.
Ash buildup is pretty bad on long cooks when you use briquettes.. lump is highly recommended and does not leave nearly as much ash.
Having said that, there is plenty of room below the charcoal grate for ash to fall and a gentle kick on the legs every few hours does the trick for me.