The P3Steel is possibly one of the better Prusa based printer designs. I recently converted my i3 single plate to a P3Steel frame and I am really pleased.
It's not all roses and champagne though - the Y Axis smooth rods are push fit into the steel plate and aren't held in place tightly. There are a few parts already on thingiverse but they were binding with the thumb screws on the bed.
Here is my solution - some clamps for 8mm smooth rods that use an M3 bolt and Nylon nuts to really hold right onto it. Put them on the inside pushed right up tight to the steel plate at either end and tighten up the bolts. Should hold them firmly enough!
Protip: print at 0.2mm layer height to make sure you get a well defined round hole and nut trap.