I thought of doing that too, but was concerned about creating another entry point for water. I found that using a wireless outdoor speaker has more flexibility and better sound quality. I have two kinds - a Rocketfish unit that has a transmitter that connects to the RV stereo through the RCA/headphone jack, and a BOSE bluetooth unit that syncs to any smartphone or tablet.
2010 Jayco 17Z
2007 Jeep Commander Overland 4x4 HEMI