Regarding the waterproofing. I've had my components for over 2 yrs now and water hasn't dropped in, knock on wood! Unless ur car has been in a accident, I wouldn't bother waterprooing. There's still a very tight seal in the door panel. But do it if u feel uncomfortable.

In regards to wiring everything, I chose to re-do all the wire and not use the factory wiring because when i sell my car, i don't want a single thing wrong. What I also notice with the factory audio wiring is that the color of the wires don't match up. Take apart the dash on the driver's side and see for urself. I'm telling u, best bet is to rewire everything just for the components. Very easy job!