I was kidding about the gravel, but I do have the psu with the fan facing upwards and it is fine, in fact, I had to rma the psu (for a different reason), and seeing as it has been like that for 2-3 months, it was surprisingly dust free.
You can use a hole punch to make the holes, and put them between the case and the fan. Make sure they are used though, or they dont work properly
