Tom, slap a magnet on the side of it and see if it sticks. Of course cheap SS will stick to some extent also.
Bob, I like Proto tools also. I only have a few sockets and they are so old the markings on the sides are just about worn off, but they still work just as well as they did when they were brand new.
Stuck like white on rice. I figured it wasn't premium SS, I mean it comes from China AND it's just a toolbox, but I did that test at the store. My little mag based light stuck to both versions just the same. Pretty sure they're the same cheap SS, one painted and one not.
Either way I didn't really care since I don't tend to roll my boxes out in the rain anyway, and I couldn't see the extra 400 bones for the "SS" model.