Hi guys! I wanted to make a cold storage system, and although what I have now (multibit on laptop, wallet files in truecrypt container on usb) should be fine, I was wondering if deleting the wallet file altogether but keeping the private key (which have been exported already to the same truecrypt container) would work for cold storage/paranoid level security.

From the multibit "wallet management" help file:

Deleting a wallet is an irreversible action known as a file "shred". If the addresses associated with the private keys in the wallet have ever been made public there is the chance that someone could use them to try to send you bitcoin in the future. Without the private keys you will have no way to spend the bitcoin.
That said, if you do not expect to retain full control over your computer (such as selling it) you may need to be sure that the wallet is unrecoverable by a malicious third party. If so, then make sure that you retain encrypted backups of your private keys.

So if you delete the wallet file you can somehow use/import the private keys to spend the bitcoin? I tried importing keys with the wallet closed- doesn't work.

Any ideas?