Deborah,
We have been keeping our colony in racks for the last year, with no problems. Most of our groups are in mouse racks that have small kitty ltter pans, and they seem to do great. We have never had a problem with them eating food above them, or had any problems with them drinking out of a Vari-flow valve stem. We do have our feeding group in a CB-70 sized rodent tub rack, and they do fine in there as well. Being that that tub is deeper (6.5 inches), we put a 2x4 block under the sipper so that they can reach it easier.

As Mike stated, they do breed very efficiently, so we typically keep the males and females seperated, until we are ready for a few litters.

I hope some of that was helpful.