That's the stuff but I didn't know Ronald Macdonald had anything to do with it.
I got my info from the body shop next door and thought I'd try it.
I just removed all the paint from metal surface using a sanding wheel (which also left the surface rough), then did the same on the fiberglass mating surfaces.
Whipped the whole lot down with acetone which cleans and de-greases the surfaces and also softens the fiberglass.
Stuck them both together, 1/2 hour later it done! It appears to be stronger then fiberglass bonding paste.
That said I am told it's now common practice in body shops bond panels on using some sort of "sticky stuff" instead of welding them on. Must be good stuff