Need Ideas for Refugium Build

Hi everyone. I have a 175G bowfront tank with a 35G sump. Tank includes about 25 different sps and lps corals. Fish include two black clowns, a blue jaw trigger, 2 tierra anthias, a copperband butterflyfish and a blue damsel. Tank has been running for about a year now and was a build off of a smaller (20G tank) i started earlier. My question is I want to build a refugium but i dont have space under my display for another tank and my sump is taken up mostly with my protein skimmer and other mechanical devices. Is there a way to make a refugium that will be external from the rest of the setup that will not have overflow problems? Any advice or ideas would be a big help. Thanks.