I did this same thing to my biocube about 2 years ago. I had a 1" bulkhead added to the bottom of chamber 3 and added a refuigum under the tank. I took the hood and stock lighting off and am currently running a 150W 14K MH light fixture. I have a seaclone skimmer in the refugium as well as a filter sock to catch all the junk. I made my refugium out of a sump that had bioballs in it but had a guy cut things out and add baffels and a bubble trap. It's been running fine and I am glad that I decided to customize it. Hope you enjoy your tank. I can post some pictures if anyone would like to see it.