This is where my outside stereo speakers are installed on my OFF-ROAD POPUP under the awning area... These are 5-inch speakers I think...
These work out great using the JENSEN CAR RADIO inside. The front/rear speaker fader slide is setup to run inside and outside speakers. Like inside the automobile you can move the slider in the middle to get all speakers to work.
My trailer uses the MARINE WEATHER TYPE speaker cones and have been great for us since 2008.
I did put a box over both speakers inside the cabinet inside the the trailer to cut down on cold air draft coming thru the speaker hole.