Could the drives get damaged? or could it shorten the life span?
They will be just fine mate in their little hammocks.
HDD's also have mounting holes on the bottom, so you basicly could screw one down to the bracket.
I do not expect that the bands are completely rigid. The moving parts might make the hdds to shake as they operate and that could potentially damage them or reduce their life span. You probably need to add sth to make the ¨hammock¨ more rigid.
I think were tackling the issue of hdd noise and movement the wrong way. Perhaps instead of allowing the drive to move you allow the entire drive cage to move and just have the drives secured to the cage as tight as possible?
That's not a bad idea although I would have to cut out the whole cage out and then rig it up for basically the same effect
The bungee cord was surprisingly rigid, but you are right there is a bit of movement, when I turn on the PC I could not see any movement at all. they seem fairly solid and they were definitely not "shaking"
That reminds me of this build I saw a while ago.
http://www.ibuilditaudio.com/Projects/computer/computer-case-4.php
haha looks cool. kudos bro. add a little drink umbrella and a bucket of coronas to finish off the effect. maybe add a little beach sunset in the back ground with a parrot.