Ram Cummins locking fuel cap

The door has a soft rubber seal that does a good job of sealing the dust out. I'm thinking their test was done with the door open. I do think it's a good idea for sure. I use the Mopar cap that comes on the EcoDiesel trucks.

I'm not so worried about a cap that locks so I've still got the plastic factory plug stuck in mine. When it wears out I'll figure out another cap but at two years it still works fine. I'm on dirt roads a lot so I'm not really a fan of the capless setup.

Got mine from Geno's Garage.