I have a Jensen stereo unit with A, B, and C. A is inside 2 speakers and C is outside - no second set of speakers inside for B. I replaced the inside speakers with 6 1/2" 3-way Pioneers soon after we brought our new trailer home almost 2 years ago. My outside speakers were very weak like others have said. I just completed rewiring and adding a second pair of outside speakers. I installed a volume control inside my storage bay just above my small fridge after luckily snaking the wires down (and up) the inside of the exterior wall. It controls both the weak tear-drop factory speakers, and a pair of old Dual speakers that sit on milk crates under my frame, and attach/detach in a weather-proof electric box and cover, with banana plugs. I ran the speaker wires underneath and inside pvc conduit along the I-beam. The volume of the inside speakers are controlled by the fader somewhere around R3. I may install another volume control for the inside A speakers rather than using the fader. I know - way too much work - but it sounds pretty sweet and at low volumes! I had most of the materials so it wasn't very costly.
2013 Jay Flight Swift 264BH
2013 Ford F-150 SuperCrew Cab XLT