I'm restoring a '63 Impala SS and had to replace the original passenger front floor pan. The repros come with slots in the sides that are there so they flex a little bit and you can be sure it fits all cars. I've got the pan all tack welded in and now I have to fill those slots. They seem too wide for a weld seam and I don't think body seam seal would work the greatest because it is a fairly wide gap. What do people usually use?