Hole in tank fix?

So I was cleaning up my tank, well scrapping off several coats of under coating, and found a hole on the top, about the size of a shingle nail. This tank hasn't had gas in it for about 5-6 years and there hasn't been a filler neck in it either. Aside from welding this thin metal, and somewhat dangerous procedure what else do you recommend? Has anyone used Seal-all? I was thinking about putting a large sheet metal screw coated in seal-all into the hole but any looking for different ideas.