Once all the underside repairs were done, I grooved out the corresponding areas on the top side and applied more fiberglass filler to repair the remnants of the stress cracks on top.
Here is the semifinished shaker dome after all the fiberglass repairs were done. Still needs some primer, redrilling of the rivet holes to the correct size, and epoxying of the door assembly into the opening, before the metal base plate can be riveted back on.
And the underside:
The before and after of the reconstructed missing edge:
