We have a 17fq and placed a folding mount on the end of the overhead cabinet above the coax connection on the wall.
Got it at Camping World. Catalog #51564.
On our trailer I use the Fader function of the radio to control which speakers, inside or out, that play.
I will caution you that it was not possible the way the wires were connected from the factory. No matter which way the Fader or Balance control were set there was always one speaker on outside.
I finally removed the panel inside the cabinet next to the radio and using the radio manual labeled everything and set it up to work that way. Good luck.
2014 Coachman Clipper 17FQ
2011 Ford Ranger 4X4