Its directly behind the tank, along side my HOB aquaclear. This tank does not have a sump....yet at least (future plans). See in photo above. Skimmer on right, Aquaclear on left, heater in aquaclear, ATO attached to the left hand side (covered by screen top). Dosing pump output will be run either to the Aquaclear or the output area back there.
I've built this setup to where every piece of equipment on this current tank, could be pulled off and used on a larger tank should I upgrade which is inevitable in this hobby. Skimmer is rated at larger tanks, lighting can carry over to a larger tank, dosing pump, powerhead, etc.