I don't know if this would be an option for you, since it does take a little re-training and patience, but I started using the dog potty pads for my ferrets. It started with our first little girl was so little a climb into the box was just too tall when she needed to go, then our first boy kept trying to eat any kind of litter we got. Although, if your problem is boys that go "up high" you'll still have that problem. I had to make a custom cage pan out of plexi-glass to solve that, but it still requires extra scrubbing.
But other than that I would say to look into some of the cat litter boxes, they have lots of options for covered ones. They even have a corner one on here I've thought about trying. I hope you find something that works for you and your fuzzies. :)