The original post pertains to speaker wiring so I'll keep it on that topic. Its very difficult to introduce radiated noise into a speaker wire like you would have with live-level RCAs. The exception would be the inductors in passive crossovers so their location in respect to engine management electronics and such would be important. In countless boat installations I can't recall a single instance in which we had to relocate speaker wiring due to noise. There simply isn't enough inherent gain in the noise source for speakers to pick it up. In contrast, you're seriously amplifying whatever minute level a line-level RCA picks up.

Earmark Marine