[Weasel9992]

If it's just FRK it's fine. No biggie. 2" will be fine, but 4" is okay too...not really necessary though.

I do agree with the "no backing" idea though...an open back is ideal. If you make them fairly light weight you can hang them from the ceiling using wire and plant-hanging hooks (the heavy duty sort). That's kind of another argument against making them 4"...they tend to get too heavy that way.

Frank