>Could you tell me how you keep the dust out...
Obviously, I don’t. However, it is not a closed container with fans pushing/pulling air with dust into it like a vacuum cleaner. It accumulates much less dust than many covered computers I see in my shop, especially towers that are put on the floor. Also, my office/shop here in Maine, U.S.A. is heated with a wood stove which makes the environment worse (but not terrible) for computers than some. A leaking roof would be a much bigger problem.
>…or if it gets in how you clean it out?
Blow it out with lungs. Larry