Well, the mount command probably failed for the same reason as the symlink; something to do with permissions. However I'd still say going the symlink route is better because once you set it up it means the symlink will always be there, whether the USB drive is connected or not (when the drive is disconnected the symlink will be invalid, but as soon as you reconnect it will still be pointing to the right place so will work again); with the remounting bit you'll have to manually remount the drive to your desired location everytime you connect it.
The permission denied thing is a bit strange, I'll have to give it a try when I get a chance to see what exactly is causing it...