Mt
My thwart is flat wood and below the gunnels so I put it on top of the thwart.  On my magic I have a 5 inch piece of ¼ ply wood fastened under the thwart which I call my dash. I have a place for pliers , those things you hold northern mouths open and my compass  + space for a couple of lures and my fish detector fastens to the bottom of it. If you have round thwart see if redrock still has the clip on compass.  They look like a plastic finger ring with a split in the bottom.  Or google  compass ring or wrist compass.
Good luck  with that knee.