if hes losing wieght they do have some products meant for rats that will help them gain wieght- i know its a green goo, but i cant think of what its called atm .my rats loce echineachea (?SP)- they have articles about it if you search for it. in theory it can help to increase the immune system.
and as a general note (not to kitty, since i know her other rat passed away?) its better to have more than one rat because they are social my rats sure do appreciate each otherse company.
i do usually bother to make a "fancy" hammock (unless i have a bunch of yarn ends hanging around)- i ussually just punch some holes in the fabric and use paperclips to hold it in place.