I cut a 1x2 inch notch out of the back corner, it works really well. I added a couple of 1/2 in. quick disconnects. so it only takes a few min. to service the filter. It's small and i have it sitting on a desk behind the tank. It keeps the water really clear and you can control the flow into the tank. No tornado in the tank.
I think I might go with a Zoomed 501 and the Archea 50w mini heater. The heater is so small I will just stick it in the tank (although it could probably fit in the filter!).
I wonder if the Zoomed 501 has 1/2 tubing - if so I think a could of disconnects are a good idea. Those have proven handy in my big tank - there always seems to be a splash of water without them