While it may be hard to see; there is a VIN etched into the passenger side frame below the passenger door, between the foot step mounting holes, just rear of the middle tub mount, on the upper half of the frame rail.
I tried using a fine grit sander to remove the rhino liner and rust to find it but wasn't able to see it. I did find a number stamped on the underside of tub but I can't make it out.