My friend suggested that once I've deleted my wallet to use the drive wiper feature in cc cleaner and set it to 3 passes, that should do it, do you agree?
Yep, I agree. CC cleaner also is a good tool.
ummmm...ok, so I'd have to load it up on another computer, confirm that my bitcoins are there, then destroy the .dat file on my computer (whilre preserving the one on my usb key obviously.) Is there another way to confirm it's not corrupt? I'd rather not have to load it onto another computer...
Well if the backup is corrupt and you deleted the original .dat you indeed have lost your money.
Not sure if its possible to check without using a computer.
If you are looking for some sort of coldstorage maybe a paperwallet or a newly made offline wallet will suit your needs.
https://en.bitcoin.it/wiki/How_to_set_up_a_secure_offline_savings_wallet provides a nice step by step howto.