I have my amps mounted in the spare tire well and got a AAA membership, but it is not an average system either. I worked as an installer for over 10 yrs and rode around most of the time with my factory radio as I just didn't want to work on my car after doing everyone elses. After I quit that job, the hobby was fun again so I decided to put the system in my car I always wanted. It took a few months and alot of planning but works great.
Here it is if you want some ideas, let me know and I can help explain.
http://www.cardomain.com/ride/2395420/1
The screws you show in the pic for the ground a small self-tapping sheet metal screws, there was no hole there before. This is a common practice although a nut/bolt will work better. You also need to be carefull to use short screws so you do not puncture the gas tank.