i would just get a filter and cover any of the fans that suck air in (dont have to worry about the PS - it blows out)
or - get a computer case (standard)
and then place it in a home-made wooden box - use plexyglass for the front panel and a rubber skirt for the galss to seal.
then mount one 5 inch fan at the bottom of the box, and another at the top (blowing out)
cover the first one with some form of filtering (one of those carbon filters for humidifiers should work) - double stack it is you have too.
that should keep any dust out - and if not - heat from the computer and the fan at the top blowing out - will circulate it out.
hell - the cheapest method -
$10 can of air - blow out the system every 3-6 months - dependant on conditions...

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Ignorance pays me money