I've started one from gumpaste but I'm not sure it'll hold up. It has to be 8 inches in diameter so it's pretty big. I suppose I could use wire in the gumpaste but I think it won't look great.

Any ideas would be appreciated!

I think one made with gumpaste and held together with RI might be your best bet. It would probably hold together with just water, too.

I have 2 thoughts for you. For the buck deer in my pics I used floral wire and covered it in gum paste then colored it. I think however that it may give you to much thickness. My other thought is to use a balloon to support the cage while it dries then SLOWLY let the air out and you should have the shell. You could use royal icing to draw the shape or even chocolate candy melts. I am not sure if you would need to rub something on the balloon so that the cage will not stick to it. I hope one of these ideas will work for you.