<P>Hi Yamsack. When converting my cargo van, I drilled holes both in the raised part and the valley part of the corrugated floor. I didn't have any problem except right along the drivers side wall floor where there is an area that has about a 6 inch area with metal casing underneath instead of just the flat metal floor. I was trying to put eyebolts in the floor, and in that area, my long bit wouldn't go through both surfaces. Other than that, it's easy. Just make sure you don't drill above the gas tank, because the bit pulls down hard when it goes through and could easily puncture the gas tank. </P>