I did this job recently. Instead of staples I used stainless steel wire that I think was about .031" diameter. I clamped the sweep onto the door and drilled holes through them both with a drill bit slightly larger than the wire diameter. I put 2 holes about an inch apart, and did that about 5 or 6 times over the length of the sweep. Then run a U shaped piece of wire through both holes from the sweep side, and then twist them together on the back side. Make sure they are nice and flat on the sweep, like a staple would be. It worked pretty well, and no harm or breakage to the door card.
81 F150 Flareside, Edelbrock Pro Flow4 FI, hydraulic roller 351W, E4OD, 4x4, BW1356
92 F150 RCLB 351W E40D BW1356 mostly stock