PSP screen problems.

Seriously, I honestly think I can only play this thing in an air tight bag. I just got dust caught underneath the screen after only a few months of owning the PSP, then exchanged it for another one which got even MORE dust particles underneath the screen after awhile, plus a stuck pixel on the lower left hand corner on an un-related note. The thing is, the dust found its way underneath the screen only a couple of hours after I got my new PSP, which I kept in the case that I bought for the first one. I took it out for only a couple of minutes and TADAH!!! Dust particles!!! Seriously WTF do I need to do to keep dust from getting underneath the screen!!!