I have the same problem as well, I live out in the country and we have big trucks /Simi's going to the Rock Quarry all day and night, the dust they make is terrible ....
My advice to is Make sure your computer Sits off the ground..Put it on a table or something, making sure it is off the ground at least 2 feet..All of my computers sit on top of my computer desk.. You have to very careful when cleaning a computer, MAKE SURE it is NOT Plug IN.... I use different sizes of paint brushes... You just want to make sure you don't Ground out anything..