That's fantastic! (I commented on your enquiry thread about this, but Hope informed me that you're not able to check here regularly)
I'm looking to do something similar, and what you've done looks very good. I don't think I'm brave enough to cut into my barred cage though... although I suppose I was wanting to put tubes in it when it was a standalone cage for my dwarfs, so it might not be such a bad thing. I think I'll buy the ferplast attachment, and see what I can do with it (i.e. if it can fit in the door in the roof, that'd be helpful). But I might not have any choice.
Although the Fantazia cage looks big, Sen has grown quite big, and I think she needs more space to run - and somewhere better for me to put her wheel (because the ones that come with the cage are too small, and the SilentSpinner I've got for her JUST fits in the bottom of the Fantazia, however I think it annoys her that I have to put a pencil in the back to keep it from hitting the curved bottom.). She chews at the bars a lot, and is constantly trying to escape, so adding another cage would help.
Did you try many different tube types with the Fantazia? I'm just not sure what fits. Someone on PetsForum said that Habbitrail, Rotastak and Ferplast (and Savic) tubes fit the Fantazia (although may need sellotape if they're a bit loose). And that Crittertrail connecting rings help...
Man so much to look into!
Might just be a case of experimenting. But like yourself at the time, money is tight just now, so I can't afford to splash!
Thank you for the great ideas though!!
Gillian (and Sen) (and sorry this is so long!)