I don't know about filler, but for my floors I put down Por-15 first then seam sealed and the seam sealer didn't have a problem sticking to the por-15, nor the top coat to the seam sealer.
As far as prep goes, for por-15 this is what I do:
- Usually paint stripper or wire wheel down to bare metal.
- If any rust is present I wire wheel it off.
- Get metal as clean as possible using the wire wheel.
- Then rough up with 240-400 grit paper.
- Then I use their marine clean (not laquer thinner or any other solvent) cut with boiling water and go over the area 2-3 times, let dry thoroughly.
- Then start with Metal ready, 20 minutes or so till the surface turns cloudy then rinse and let dry.
- Apply por-15, allow to dry till only slight finger drag.
- Now a 2nd coat of Por-15 same deal with allowing to dry.
- Then seal if needed then top coat.
Works very consistent now. I was still apprehensive about doing my floors (since I spent so much time cleaning them up) but I really scrubbed the heck out of them in step #5