I am very happy with a seperate sump and refugium. My refugium is a nearly clear rubbermaid type storage container (about 30 gallons). It sits on a metal rack type stand in my cabinet to be elevated about 8" from the floor of the cabinet. This way it just gravity flows to my sump (a small glass aquarium) that sits next to it via two bulkheads.
This way I can keep all of my equipment seperate from the plants, sand, critters and rock. My sump houses my skimmer, heater, carbon and return pump. Sand can be very harsh on pumps.
Good Luck,
-Christine