I've had horrible luck with the health of my ferrets. First I got Munky and Mishka. Mishka died about 2 weeks after I got her home for unknown reasons. I got them in Arizona and was living in California at the time so I felt like I had no recourse. A month later we went to Vegas and I picked up two more kits, Pipsqueak and Sasha. Fortunately none of them fell ill while we were still living in California, but shortly after we moved to Texas Munky was diagnosed as adrenal. Poor thing lost almost all of his hair, and developed a couple of mast cell tumors as well. He responded well to the Lupron, so we've kept him on that instead of surgery. About 4 months later Sasha became adrenal as well, so we went the same route with the Lupron. A few months after that she started grinding her teeth and my vet couldn't figure out why. I started seeing a different vet in the same hospital, and he found a large hairball in her stomach. At her pre-op bloodwork it was discovered that she had insulinoma. I was going to have her adrenal tumors removed since she was going to be open anyways, but my vet advised against it as he said the recovery would be much more difficult on her. She only lived for nine more months, passing away at the age of 5 years old. One month after Sasha passed, Munky was diagnosed with insulinoma as well. A few months after that, Pipsqueak was declared adrenal. Munky has had two crashes from his insulinoma in the past two months. The first time I found him completely unresponsive in his cage drooling. The vet stayed late for me and they were able to save him. About a month later at their next vet visit I asked the vet to increase his lupron dosage since he was starting to lose hair again. When I got them home I took them out of the carrier to put them back in their cage for a bit, and found Munky drooling and slightly unresponsive. Luckily he wasn't very far gone so the vet was able to talk me through bringing him out of it at home. I can't imagine not having ferrets, but at the same time I just can't deal with insulinoma anymore. More than anything that's what has gotten me to plan on phasing ferrets out for a while after my current bunch is gone (with the exception of one more so Charlie has someone to grow old with). I can't even express how much I hate this disease.
I started out with superpet cages too. Those things were horrible! Most of my clips broke, so I just used cable ties to keep the bars together. If I tried removing shelves, I'm almost certainly break a shelf clip putting it back. I love my Ferret Nation!
ETA: Munky was a silver mitt when he was a kit, he's now almost completely white. He has a few sporadic dark hairs mixed in on his back though.
