I hard mounted my Leatherworks bag last year. Don't forget locktite on the bolts.

The ultimate setup would be to use quick-release pins (like on a hot rod hood). Then, you could pop it off in a minute for cleaning. I wish somebody smart would figure that out so I could copy them...

 

I just put a plastic bag over mine when washing the bike.
I do the same to my Danny Gray seat and the Heavy breather.