I finally got an ATO hooked up. I decided not to go with the RO/DI method but instead I bought a 30g water container which should last about two weeks before needing to be filled. The container and pump are in a closet on the other side of the wall from my tank. I went with the Tunze ATO. Here's some pics:

Dual float switches in my sump:



Freshwater line going into over-flow. I tried to have it go into the sump but it was creating a syphon.



I used some plumbing supplies from home depot to make the hole in the wall nice. I wanted a decent sized hole in case I wanted to add a dosing system at some point. I didn't just want a nasty looking hole in the wall though.



Finally, the 30g container in the closet.



I really like the Tunze ATO. I feel pretty safe using it since it has dual switches, one optical and one float switch. It also has safety features that prevent the pump from running dry and shuts the pump off permanently if the pump runs more than 10 minutes.

Once I get a couple automatic fish feeders, I can go out of town for a few days without having to worry too much!