i filled all the big holes with steel sheet metal i bought from my local metal shop. I welded in the patches and then cleaned up with a grinder. The biggest job was closing off the heater motor hole. I basically welded a plate on the back of the firewall and then used a very big holesaw to cutout a plate to fill the hole in the bay. Once everything was welded in, i smoothed with my grinder and then filled with rage gold body filler to smooth. I stripped the entire engine bay with my da sander and used the needlegun for the hard to reach areas. For the final surface prep i used kustom shop grease and wax remover from tcp global and then shot etching primer, then urethane primer for the whole car. Hope this helps.