The cardboard mesh is getting close to tunnel 2.

I drew hill contours (where it hits the wall) on scraps of cardboard, cut out their outlines then transferred the pattern to pink foam.

I hot glue the mesh to the pink foam which I screwed to the wall (making the hills removable without much wall damage). I put squares of masonite under the screw heads to keep them from sinking out of sight in the foam.