Slide won't come in

I had a similar camper to yours with same problem. Turned out to be the gears inside the slide motor. You can access slde motor easily even if enclosed underbelly. it's prob just coroplast which looks like black cardboard underneath. It's only held on by screws so just remove them and you can get to the motor. If the underbelly looks like tarp material yes you would have to cut a small flap into it to access the motor. My motor was made by venture mfg which makes a lot of motors for the rv industry. They are plastic gears and were easy to replace once you open motor up.