I have a highly optioned 2013 RTX that I just purchased used. It has a trunk mounted kenwood tuner and amp with a remote control pod on the dash. The older Alpine speakers sucked and I'm using Polk MM522 5.25" in the kick panels and MM652 6.5" in the current locations by the seats. They are marine rated, as is the tuner and remote. Therefore the should withstand some moisture if you get rained on or live in Florida, like me. Crutchfield or Amazon carries them.
That said, I just installed a set of Infinity reference series coaxial speakers with a JBL power amp and a JBL 8" powered subwoofer in my '69 Z28. The JBL Sub will fit behind the passenger seat or driver's seat of a Cobra, btw
I don't think you would go wrong with Infinity, Polk and or JBL.