Here's a picture of the one we made:
http://trailmanorowners.com/forum/album.php?albumid=42
Luckily I haven't had the chance to try it out!
Just looking at it and the spray foam I put into the area around the pipe where I thought mice could get in, I wonder if it would help to spray foam all around the plumbing inside the cage (I'd have to put a backing on it to hold it in). We used spray foam when we put in the wheelwell retrofit and even though we've had two blowouts, the foam really protected the cabinets. It wouldn't look very nice, but if it would help...it might be worth a try. Maybe we could put a sheetmetal liner around the front, or something?