scotch it with silicon ex, wipe it with paint shop towels and silicon ex. close all the holes . use 2k epoxyprimer not rattle can! fill sheet metal gaps with a brush if necessary. allow to dry for a week. scotch the primer and clean with silicon ex. seal the gaps with sprayable and paintable highflexible underbodycoating. give in the wheel areas a structure coating. if you wish you can use it for the underflooring. i would stop at transtunnel / firewall seam. engine bay only 2k epoxy.