Yes, I would provide an access hole for the cabling. Much the same as the holes for the bolts into the wall. I will certainly look for a mechnism of sealing it properly and put it on the wall side of the safe, to minimize the risk.
However, I don't want to manually do anything ... if I have to do something then it ends up not happening ;-) I want automatic backups to a device in my safe.
* the drive must go into powersave mode,
* or via the usb to cradle i should be able to say "power off/on",
* or via a usb to a plug unit which i can switch on/off via usb/serial...
Or maybe in a big gun safe the heat will not be an issue at all? I can't find minimim volume statements on the drives either...