Hi,
the way i did it on my F27 was this:
-select the polys of the fuselage section you want to "cabinize"
-use edit/clone to create a copy of the fuselage section
-select the cabin polys and add a normal modifier from the stack
-check 'flip normals' in the parameter rollout, to make the polys visible from the inside.
-if necessary create a polygon to make a cabin wall at either end.

After this you can apply the texture, which is not really something i know very well. Hopefully this will get you started. 

Oh, and if you like your fuselage to have some thickness, you can non-uniform scale the cabin to make the diameter a bit less than the exterior fuselage.

Good luck!

Willem