Thinking a little differently. Was trying to reinforce the wheel skirt from the inside...why not the outside instead? Had some ½"CPVC (pex tube/pipe) around so I decided to use it as my hinge and exterior support. I will paint after I git it fabbed up.
The white stuff around the wheel well is a plastic corner bead fer archways. Costs about $3.
Mock up of the hinge/support bar...
Rough fit...
Gitting there...
Top view...