Doc,
If i understand you correctly, the flanges are the 'wings' that are integral to the overhead hatch itself. If so, I would suggest finding a fiberglass material supply co. near to your locale. Or call Fiberlay here in Seattle. These guys are walking encyclopedias on repairs. They helped me a great deal on closing up 2 below water line through holes. Depending on how much repair you need to do, you may get by with using the fiber putty alone. (It's chopped fiber already mixed with resin and only needs the harder added when making a batch). It's just like using putty or bondo. Anyway, with a bit of guidance and suggestions from the pros that sell the stuff....you should be able to take on the job. Good luck,