Elantra....yeah..it's best to weld the opening shut, but that depends on a couple of things.
1) If you weld the opening shut, you'll almost never be able to go back to having handles or the antenna again, in the stock positions. Most people never would put their stock handles back in or whatever, but ya never know.... :hmmm:
2) Welding gives you better brace. Basically by only fiberglassing the area WITHOUT welding, it's easy for the area to crack and/or spiderweb. Welding in a steel template over the area re-inforces the area and makes it solid.
It's alot more work to weld the areas, and shops would charge more, but it just depends on how involved you want the project to be. To be perfectly honest, I would (and I always do with my customers' cars) weld the handles shut, but as far as the antenna goes, it's not neccesary to weld that small of a hole closed. You could just fiberglass over it. Good luck...

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