FYI, If you are going to make your own rear speaker mounts, I have found a very cheap part at Home Depot that will make your life easier to mount the speakers. After cutting the holes by hand on my mounts, these worked great, and were only about $1.50 each.
After mounting, scuff with scotch pad, then paint.
Found in Electrical section at HD>
3.5" speakers fit PERFECTLY, and great to attach, no rattles!
Disclaimer: I am by any means not an audiophile, so please no comments on my choice of "cheapy-deapy" speakers. They were super-ultra cheap on Amazon, and if and when they blow, I'll upgrade for something else. I had to justify possibly cannibalizing them before even knowing what my end result would be.
All in all, I am pretty happy, it "fills" the back sound enough (I have them directly connected to HU, since I only have 4 channel amp). Definitely adequate, no complaints.
For speaker connection, I did one run of 16g 2 pair cable thru the center console, and used a MOLEX plug so I could "quick disconnect" the rear enclosure when I needed to access the engine.
