'rolling' rear arches

Just after some quick advice. I'm pretty happy with the metal bashing side of things and the fact i'm probably going to crack the paint, but could do with a bit of advice on the prep and sealing before and after. Obviously a good wash first to get rid of the muck, but do I then need to remove the underseal before i knock the lip up or do i leave it in place? Then I'm assuming semi struc. seam sealer to finish it off? A fairly quick, knowledgable answer would be much appreciated :thumb: