Hi Nigel, I have just reached under my desk and felt the power supply, it is as cool as a cucumber, (after 5 hours use ) and the screen display is still perfect, so I shall now try putting the sides back on.

maybe it's the top panel that is the problem, it could be preventing the heat from the power supply from dispersing.

I am not worried about dirt collecting, I have a very efficient compressed air system which will blast out any accumulated crud.