Another bodywork question

["Dr T. Dafforn" <td214@cus.cam.ac.uk>]

Heres another question about my impending journey into body work
protection...
There are going to be areas of my spit's body which will need a little
filling (my welding skills arn't perfect yet)...
Now the question is, do you apply filler to bare metal?
I've seen, during the restoration how water seems to get under filler
somehow and rots the metal from the inside...
I don't want this to happen..
So I was wondering wether its is worth painting zinc rich primer over the
area before the filler was added, to protect the metal..
Will this prevent the filler from sticking???
or am i just being too paranoid about rot?
                        Cheers
                                tim

Decapitated spit 1500