nobody knows the best way......
Heres one of the most comun ways. I talked to my uncle who has owned an auto body for 30 years and he said this would be a very good way to do it:
1) Grind down the moulding so it is flush with the door panel
2) Depending on what is left after the grinding, if needed use a pice of plastic with tons of small holes in it to somewhat fill the hole
3) Use drywall screws to hold it
4) Using fiberglass resin and schreded fiberglass mat (like hairs about 1" long), fill in the remaining gaps
5) Sand with a medium coarse paper to remove areas with way to much fiberglass, Sand with a medium paper to "level out" you work area, Sand with a medium fine paper to smooth out your work area
6) Using Bondo-Glass or a similar "kitty hair", create a "skin coat" about 1mm thick over all you work area
7) Sand with a FINE paper to SMOOTH out and minor imperfections (with a FLAT sanding block of equivalant) trust me, if you sand with your hands, you will end up with waves on your surface that are near invisible untill after paint is done!!
Steps 6 and 7 can be repeated several times untill you have no dimples or waves and a perfectly flat surface. *Try using a ruler placed horizontally on your work surface to determine how good it is
I'm going to post this in Tech with some diagrams shortly......
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3.4DOHC/5speed swap coming soon..(gathering part's now!)
We work with the Fieros a lot but also have a custom paint and body shop and do full mechanical, not just the Fieros although they do seem to be taking over the shop 
