I need to make an extruded cut on a lofted and shelled part...I originally built the part (attachment loftedbookbox2) as a lofted solid and then made a lofted cut to get a "shell" effect, but that resulted in thickness variations. Then I rebuilt the part as a lofted solid and shelled the inside and built bosses and other features inside (loftedbookbox070808) ...that one is working out just fine, but I need to make a cut out of the front. i'm struggling with both. Someone pls help!!!

This is a plastic book box that goes under a student desk.

The corners are conical and the walls are non-planar and the base is flat.