Skimmer in the first chamber -> refugium in the second -> return in the third. Would build the sump with 1/4 in glass baffles. First baffle all the way on the bottom. Then I would put the second one after the refugium, 1 in from the bottom and 1 in away from the last baffle that would be on the bottom. That's about it.
30g Long Frag Tank
3g Pico Reef