Having not seen a picture, I am inclined to agree with Lumatic that a patch may be the preferred way to go if the hole is big. If it is small I think that I would try to fill the hole with a rivet if possible, before bondo (plastic body filler).
If the light is centered above the door like the one on my 76 I would make an oversized oblong patch. Center it over the door and rivet it in place. Then install the light in the patch center. The use of countersunk rivets and bondo would all but make the patch invisible, but I've seen some patchwork with bucked or Olympic rivets that actually look good and add character.
Please post a picture or two when you're able.
Oh and welcome by the way.
"You wouldn't worry so much about what others think of you if you realized how seldom they do."