That's such a neat hammock. My rats never liked the hammocks I made them :-(
My ratties got respiratory disease (mycoplasma?) also :-( I had one of them on antibiotics when it got bad, but it was so hard to give it to her without her spitting it out that I don't know how much she actually ingested.
I heard it's hard to get rats that don't have respiratory problems, it's so widespread.