Hmm... remind us, what was the timeline of when you installed the coilovers, camber arms, and sway bar in the rear? All at once? And when did you start hearing the sound?
Since you've been troubleshooting this for a while I will make the assumption that you've already double checked and there's no loose bolts you forgot to torque. Instead of checking torque each time, grab your wife's nail polish (or yours, I won't judge) and make a mark across the bolt/nut/part so you can tell visually if it has loosened without needing to put a wrench on it.
Have you taken a close inspection of everything you can see, to see if there's any evidence/witness marks anywhere from contact? Fenders, wheels, knuckles, control arms, subframes, sway bars...
Have you checked the KISS stuff? Spare tire snug? no loose stuff sliding around under the rear seats?
Have you had a helper sit in the rear of the car and try to pinpoint the sound (or drive while you search for it)? If you can produce the sound at low speeds safely and you trust your driver, drive with the tailgate up and hang your head out the rear searching for the source (don't let the tailgate crack you in the skull)
Can you identify more specifically when does it make the sound? Two wheel bump (speed bump)? Roll (right or left)? High speed? low speed? High frequency inputs (bridge expansion joint)? Low frequency inputs (big dip in the road)?