Rip a 2X4 down the middle and attach it to the metal upright with self-drilling screws. That's the simplest way to provide a place to drive wood screws. I'll be doing something similar when I frame out the interior walls of my shop, but the PVC electrical conduit is going to go in first. One entire 40' wall will be dedicated to machine tools, so there will be a fair amount of electrical work involved.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!