Theres basically two ways you can do it, you can lay some fibreglass over the inside of the hole and then top it with bog or you can weld it. The glass and bog method will work nut it can pop out for no reason or allow moisture in to rust the panel. Welding it is preffered but can be a real headache if you get too much heat in the panel causing shrinking and warpage. If you weld then you have to be really careful of the amount of heat you put into it, one way to do this is to get a piece of copper pipe and hammer one flat, use the flat end as a backing for the hole and it will allow you to lay a weld across the gap and absorb some of the heat at the same time.
Hope this is some help