When I had a 29 setup I used a 10 gal(only tank that would fit under stand) as a sump and I made my own overflow box. You can use a 10, 20h or maybe a 20L if it will fit. I made the overflow box from 2 lee's specimin containers connected back to back (about $5-$7 each). I bought a siphon u-tube on ebay ($7.25 shipped). You drill the inner box to the water line you want in the display. The outer box you drill the bottom for the drain to the sump and drill holes in the pvc above the bottom of the U-tube to keep the siphon in the event of a power outage.(I used 1" pvc).
The only bad thing about this is the look of the box in the tank and you have to watch the siphon for air bubbles. But without drilling its easy and cheap.
her are some old pics
This one is a full tank shot you can see the inner box up to the left
<a href="http://photobucket.com/" target="_blank"><img src="http://i68.photobucket.com/albums/i36/ccoons43/DSC00886b.jpg" border="0" alt="Photobucket - Video and Image Hosting"></a>
This is a close up of the inner box
<a href="http://photobucket.com/" target="_blank"><img src="http://i68.photobucket.com/albums/i36/ccoons43/DSC00894b.jpg" border="0" alt="Photobucket - Video and Image Hosting"></a>
this is the outer box
<a href="http://photobucket.com/" target="_blank"><img src="http://i68.photobucket.com/albums/i36/ccoons43/DSC00916b.jpg" border="0" alt="Photobucket - Video and Image Hosting"></a>
The pics are not that good. but they are all I had of the box