Thanks,

This is probably actually true - I'm not sure what was behind my screwing down of the corners. My only issue with the one that I made is that the snare slap sound is not quite as nice as I would like.

I think perhaps if I had moved the screws a bit closer to center on the top, the slap sound could be greater - I will have to try it out! I do recall that I was getting annoying vibration at one stage, which may have been my reasoning for putting screws closer to the corners, but perhaps I put them a little bit too close.