I cut 2 patch panels from a banged-up donor fender slightly larger than the cutouts. Then, I trimmed the panel until the bottom and back edges were a good fit.  Since the area to be enclosed involves several angles, the remaining sides were trimmed as needed during the install.   From a template, I marked where the T-nuts needed to be and holes were drilled.  Here are the two patch panels with the t-nuts installed.  I picked these up at a local hardware store and tacked them in several places.The panels were now ready for installation