If you want an external, non HOB
, you'll have to run it in a sump and do some plumbing. If you go to the DIY forum, you can look at a lot of threads on the subject of DIY sumps/refugiums.
If you don't want to mess with plumbing it and gettings a sump together, the AquaC remoras are nice HOB
skimmers... You would just the regular (I think it skims up to 75 gallons). I got mine through craigslist in pristine condition for $80 rather than spending the $225 online but I had to wait for 3-4 weeks for it to come up (I got the Pro version, regular is ~160ish I think).