I had hairline cracks in the upper corners of the rear cap on each side of the cabinet.
Remove the overhead cabinet and fiberglass the cracks from behind. If you support things so the crack is minimal while glassing i would not attempt to do any more on the outside because of color matching.
I had to cut a wedge section in the sheet metal ends of the cabinet to get it back in place once the fiberglass set up. I cut and installed a false panel at each end to cover the cut metal.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles