I wouldn't even put rubble back there. I think that itself is also a detritus trap. I do have 3 mangroves growing out of the back of mine right now. Other than that I have a heater, the pump, controller probes, and a media bag with carbon/GFO.

I like the rimless look of mine. I don't have the filter area covered. I don't really think my tank stinks....but it could be just me.

But if you want HQI parts, I have the rimstock (cut before the back filter area) and the covers for the back chamber. I even have a mesh screen top that fits on top of the hqi rimstock to keep your fish from becoming fish jerky.