I've found two pics showing guns removed from P-47s.
One shows a camouflage-painted training unit aircraft, with the two outboard guns on each wing removed, the other shows the well-known, 'war weary' two-seat conversion 'Category E', with all guns removed. In both cases, the ports appear to be covered with individual, contoured, round, flush-fitting bare metal 'blanks'. If this system was also used on the SAR aircraft, which is likely, they may or may not have been painted.
A third photo shows a bare metal 'bubbletop' aircraft, post war, again with the outboard guns removed, where the two ports appear to be covered by a single piece of material, rectangular in shape. This might be fabric, although it has the same tone as the surrounding bare metal, and is shown in a B&W photo, so difficult to tell if fabric or sheet metal.