http://96.31.76.198/vbulletin/showthread.php?t=78317
This 20g is skimmerless. Just runs on a AC 500 or whatever its called now. Run carbon & GFo, plus change a few gallons of water once a week.
Just thought to show you an option perhaps. If skimming I would go with something like the Deltec MCE 600. I would prefer Tunze but it takes up take room but so much more fool proof.
If you decide to sump it, {lots of nice 20g nano type tanks with sumps out there}, then would for sure I would drill it.