As I recall from looking a various photos of stone guards for one of them the piece on the wall of the trailer was a widely available awning
extrusion. Then they used an interface extrusion that slid into that channel. Because it is a rounded shape it acted as a hinge. They did put stop screws into each end to keep it from sliding sideways.
A hinge knuckle from a hinge that was taken apart is one potential interface piece coming from the frame of the stone guard that could fit into the awning
extrusion channel. There are hinges made with removable pins that can be in hardware stores. They are sometimes called loose joint hinges. There are also lift off hinges. All of those would work as they provide a knuckle at the end of a flange with holes drilled into it. You can get them in stainless steel.
This is a very simple solution using widely available parts. Not my invention, I am just reporting on how I saw it done.