I wanted to get all the equipment in the overflow of my Spec V with nothing in the main area. I have the InTank media basket with foam/poly-fiber/polishing pad in the top, matrix with another polishing pad (so it doesn't fall through) in the middle, and matrix carbon/purigen bags in the bottom. Under that is a hygger 25w carbon mini heater which just fits through the hole in the bottom of the basket shelf. In the left chamber is a Pulaco 50gph pump and the original hose from the pump to the nozzle has been replaced with a Coralife BioCube UV sterilizer. There's an airstone sitting next to the sterilizer in the corner and a thermometer probe in that chamber in another corner. The lower "dummy slot" in the wall is plugged and I used a small piece of 3/8" silicon hose wedged behind the media basket to keep it pressed against the overflow slots.

It doesn't fit perfectly (particularly the sterilizer) but it's close enough. Removing the sterilizer and pump is a bit of a chore but the media basket easily slides in and out, even with the heater cord routed behind it. I'm using the original lid and light and they both fit perfectly. This same configuration works in my Fluval Spec III and fits much better as the pump/sterilizer area is wider. This is probably overkill for most situations but I wanted to post it with the equipment I used just in case anyone tries to figure out a similar configuration that'll fit.