[dsraven]

looks pretty good. when applying the filler it is good if it goes over the primer with no bare metal. the filler is like a sponge and holds moisture so the primer is the seal between that and the metal.
for long straight things, like doors, I try to use a long stiff sandpaper holder and some of those long narrow sanding strips available at the body shop supply. actually, I use a piece of 3/4 plywood for the sanding board and simply staple the paper to the top side after bending around the ends of the board. with little pressure applied, so the metal doesn't spring away, the panels will come out very smooth and straight. there is also stuff called guide coat that is handy. it is a darker color than the primer and sands easy so it will show up any high spots right away when sanding.