I was planning on doing something similar but good luck finding a hardware store that has metric sized carriage bolts that are large enough. I found somewhere who had them on special order but it would bump up the cost too high considering I was trying to DIY. I used this guide but doubled up on the rope clamps:

http://www.m3post.com/forums/showthread.php?t=344210

it's solid as **** is completely flush and looks identical from the front, however I'd suggest keeping a wrench in your car in case you need a tow. I have no pics of it on my car, I'll snap some whenever it warms up a little and my 3 isnt gross looking.