Since the location of several pieces of hardware on the firewall are in inaccessible (from the cockpit side) or almost inaccessible locations, I decided to use rivet nuts (rivnuts) to mount some of them. I picked the largest rivnut size, which will take AN3 hardware.
In photo 1 you can see one rivnut installed at the left, and the second one being installed with a $20 rivnut installation tool (from AC Spruce). If I were doing this for a living I'd get a good tool; this one is tedious to use, but works perfectly well considering I'm only going to put in about 10 of them.
Here are two web sites that shows how rivnuts and this tool, work: http://www.youtube.com/watch?feature=endscreen&v=j637MlgO9os&NR=1 http://www.youtube.com/watch?v=dkPhGIaPCVs