My go-to is the
Emdom/MM TNT GYM Bag. Really looks like a gym bag, unlike a lot of other "covert" cases, which might not look like rifle cases, but just look weird. The bag is padded to give it structure, eliminate printing, and protect its contents. There's a zippered sleeve for the lower that is held in place by hook and loop; the end user can position the sleeve at whatever angle is desired. The end pockets are functional, but the main compartment of the bag can expand into those pockets, allowing for more internal volume without increasing the external signature. I have mine set up similar to what's shown in the stock photos below—upper on one side, lower in the zippered sleeve, chest rig on the other side.
Images courtesy of Military Morons.
An excellent companion for these breakdown style cases is the
Raven TopStop, which keeps the lube from the getting all over your bag, prevents the BCG from falling out, and keeps dirt and grime from getting into the upper. This does add an additional step to the reassembly process, so it may not be the best idea if rapid deployment is a concern.