Yep, there are some support bars in there, and the PCB and fans are are screwed to the keyboard tray. The underside - the cosmetic part - is all cover, no real structural value. Much like my old Dell D505 - the case under the keyboard was the carrier (and was a cast aluminum part).
No support bars, and you do realize the keyboard is part of the structure, right? Have you seen what a normal laptop disassembly looks like? Metal plates and supports everywhere within a plastic case that still creaks when twisted. This is monocoque, an aluminum shell that the computer parts attach to, no other support. They keyboard side is where most of the stuff attaches. The back is a shell that screws onto the keyboard, providing protection and stiffness.