Does your 08 sport 22 have the same center ceiling panel like on the earlier (70’s) models? On ours, the wiring harness runs down the center of the trailer, above this ceiling panel. While it’s still a pain to remove, it would easier than removing one of the side inside skins. You could access the wiring harness, and find the speakers wires, and then tap into them. Then all you would need to do is run them down inside the side walls using an electrical fish tape or even a wire coat hanger if it’s long enough. Cut a hole where the speaker will mount after you’re sure you can fish the new speaker wire down far enough without running into any cross ribs.
Hopefully that all makes sense and is helpful.