I own one of those Gator cases. It fits a P Bass just fine, and it's a perfectly nice case; if I ever had to get another low-priced but durable hardshell case I'd probably get another.
But fwiw it pisses me off to no end that Gator describes it as "ATA-approved" ...or "ATA" anything. First off, the ATA is not in the business of "approving" anybody's shipping containers. They simply provide lists of recommendations depending on intended usage, and it is then encumbent upon any case manufacturer to be able to demonstrate that their product meets or exceeds the ATA's recommendations.
Moreover, unless you explicitly note which ATA recommendations your product is in compliance with, the term is completely meaningless. I know for a fact that that Gator case does not meet or exceed ATA Spec 300, Category 1 -- which is the ATA specification most commonly cited regarding reusable shipping containers for musical instruments or electronic equipment going on tour via planes, trucks, or buses -- because ATA Spec 300, Category 1 explicitly notes that all handles and latches must be flush with the outer walls of the container when in the closed (travelling) postion.
Sorry, just a nit-picky soapbox issue I have!