Yes, Carl you're right. They are vented caps but the valve that vents the cap fails frequently. He'd probably buy one that actually worked.
The part number for the TF and AD truck caps is the same so he'll have to find a cap with the same locking ears that isn't vented. You're probably going to have to dig through boxes of gas caps to find one. Unfortunately parts stores don't carry a lot of these style caps anymore. They're all modern plastic ones.
