Stop in for a cup of coffee

the underside of the roof is rough side of the tongue and groove boards - hell, I'd paint it if I thought the paint would stick..
Not really sure what you are trying to do... If you clean it, blow it out, it should not continue to 'make' dust. Even if you cover it, the new surface will eventually be covered it dust. Now if you box it in, it may have less surface area and coating could be smoother- that could keep it from retaining as much dust and make future cleanup easier.