Restoration of a German M40 helmet Part 2

The first thing I wanted to find out is how to close the holes in the helmet.  There are several options like fiber math's or Body filler but that was not really what I liked most. I started to ask around and discussed the matter with my fellows who are car restores in their spare time. One of them suggested to repair the crack and the hole by welding them, see this example on how its done on youtube: https://www.youtube.com/watch?v=TmS6Ec0NzXQ
The pictures below show the result:

The first thing I wanted to find out is how to close the holes in the helmet.  There are several options like fiber math's or Body filler but that was not really what I liked most. I started to ask around and discussed the matter with my fellows who are car restores in their spare time. One of them suggested to repair the crack and the hole by welding them, see this example on how its done on youtube: https://www.youtube.com/watch?v=TmS6Ec0NzXQ The pictures below show the result:...