You probably don't need one. Having said that I run one on my 40 breeder that does not have a sump. If I had a sump I probably wouldn't run the skimmer to be honest. When I turn off the skimmer for a couple days a film will build up regardless of how much surface agitation I add. Skimmer on and it is gone. So it works. I run a CPR Bak Pak that I've had for years now and continues to work.
Post 326 in this thread will show you a 3d printed skimmer:
http://www.reefcentral.com/forums/sh...r#post25211612