The interior skins work like the flanges on an I beam to strengthen the ribs. The design is a monocoque design based on Airplane design of the 1930's. It was originally taken from the designs of the Martin Aircraft company. I would not remove the interior aluminum skins. The fact that you occasionally find that interior rivets, holding the interior skin on, have been sheared to abusive treatment on the road, indicates to me that there are stresses at work between the ribs and the interior skins. Removing the interior skins will remove the possibility of the interior skins adding to the strength and rigidity of the trailer shell.