I use the same method.. In metal areas, I drill super tiny holes and press the staples through, and then bend them tight on the other side, On areas that already have holes stapled such as a radiator support, I take a different approach, I take out the old staples for re-use, put the new rubber over the existing holes, then go on the backside and re-create the original holes areas by marking it in the rubber on the backside of the rubber where the original holes are accessable, then I just re-create the holes in the rubber in the correct areas, and push through the original staples and re-bend...or use new staples and bend them...works like a charm...and you utilize the original staple holes to boot.
Tony K.