I have an amp under both my seats in one car. My inputs are at the front of the amp and everything else is in the back. I just ran the wires so they were tight and held it in place. You could use screws though.

 

How do you route the RCA wires to the amp under the seat? Through the center console?

And how did you route the speaker wires? Did you took them back to near the HU and connected them to the stock wires, or did you replace the stock wires completely?

 

BTW I found a thread related to the Pioneer grounding problem:
http://www.diymobileaudio.com/forum/...ad.php?t=13889

Apparently, the grounding problem is the result of some tiny fuse in the output circuit blowing because it is too sensitive. Grounding the RCAs with the wire is a band-aid to the problem, replacing the fuse with a 1ohm resistor is the real solution. Might be helpful if you get noise again.