What he klhansen said! 100%! Seriously take a look at the work he does by clicking the photo links. Someone who really does nice work! Well done!
Great product but it is still a polyester filler. It and fibreglass filler should never ever never ever be used to fill a hole in steel unless you want to do it again after you paint it.
The only thing we can do to repair a hole in steel is to use steel by welding in a patch.
I like the other kind of all-metal to fill holes.
before after 
Any other attempt to "fill" a hole will fail 100% of the time.
Fibreglass filler works great on boats, hot tubs or corvettes only.
