No, no, nooo...
Okay, the piano hinge is SS, but the bumper and the plate aren't. If you place rare-earth magnets on the bumper itself and then let the plate hinge down to them they will stick. My plate is aluminum. I imagine that yours is as well. Attach a nut and bolt through the lower holes in the plate and position the rare earth magnets such that they are located where they contact with these nuts/bolts. The greater mass (I'm no engineer so don't quote me) of the bumper steel will hold the magnets better than the small mass of the nut/bolts on the plate. When the plate is acted on by the ground or rocks it will be pulled free and swing up. Once the obstruction is gone the plate will swing down and catch on the magnets again. Done deal.