>>498286A few minutes putzing about in Blender. Obviously it's not fully textured.
Make a plane, overhead view, subdivide so you get a vert in the center, delete all but upper right quadrant, put on mirror modifier with "clipping" turn on.
Extrude, move y, move x (because clipping is on, you'll get an l-shape around the original plane). Then change to a side view and move z to get your basic shape.
Add some loops where the tabs will be. Extrude down along the z for the flaps. Put another loop for the top of the tabs, then delete the faces where the slits are. Move the bottom of the flaps inward.
Subdivide the bottom edges closest to the corner (this makes those faces 5-sided Ngons), move those where you want the bottom of the flaps to be, then delete the corner vert. Remake those faces using the verts you added when you subdivided.
Add whatever support loops you need. Mark your seams.
Remove doubles, then add a solidify modifier (make it thin). If everything looks good (add a subdiv surface modifier and set smooth to check), apply the mirror and solidify.
Unwrap however you like. I found that with this shape, projection from view worked really well.
Add the hooks and any internals as separate objects.
