hmmm... no my reply isn't way off... duct tape is made to be stretchable so it forms to whatever you're taping better. packing tape while not as thick as duct tape can be made strong if you apply a couple extra layers. while this may not be the right way to describe it, i'm going to say it has a better "tensil" strength. If you take a strip of packing tape and a strip of duct tape and put equal force on each (pulling the ends), the duct tape WILL STRETCH! the packing tape will only break if you put an excessive amount of stress on it or if you compromise it by cutting into it.
try packing a heavy package and taping up the box with duct tape... ITS GOING TO STRETCH!
I've used duct tape in many things, i know a little bit about how it works.
Oh and by the way, i never said it doesn't work... cuz i have my deck held in partially with duct tape also... and yeah, mine is still in there fine... i simply said, it cannot be relied on to tape things tight. the reason it is holding well is because its so damn sticky, and there isn't much stress being put on it in the first place, unless you like to try and yank out your head unit for sh*ts and giggles. the thing is just sitting on top of the tray.
anyways, this is off topic, so on with the original topic.
~good day