Hi Will. I hope you don't mind me sharing my experiences with aquariums on your thread.
I've been using aquariums as rooting chambers for 4 seasons now. They have worked just fine for me. It's basically the same as many others do when using plastic sweater boxes, etc. The one advantage I like is being able to see into them without removing the cover. Still becomes somewhat necessary though because of the condensation on the sides as well as to let things breathe a little.
I also kept the bottom of the tank wet and elevated the cups so they wouldn't get soaked in the water. I used layers of newspaper in the bottom to help hold moisture longer.
Here are a couple pics of mine from the 2009/10 season. As you can see, I'm not afraid to recycle anything that makes a suitable container ;-) :
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