Need help on mounting radio.

I haven't completed it yet, but I plan to mount the amp in the trunk, rear speakers only (maybe front), place my MP3 player in the ashtray and run the cable all the way back to the amp. I've seen the MP3 to RCA jack cables up to 25 feet. Think of all the wiring that will be avoided. Although my dash was hacked some, I have the original AM radio in there now. With the MP3, I get FM radio, 8 gigs of recorded music plus it hold videos...that way I only have to do one burnout and every other time some smart a** says something, I'll show the video....reduces the risk of tickets.