I had the same problem with my mum last year when I wanted to bring joey inside. However I got passed that because he was 8, and we where forecast a really bad winter. He was going in my bedroom so if he made a mess, my mum wasn't bothered :lol: the issue was hay getting everywhere, my bedroom is in the loft and hay worked it's way down 2 flights of stairs!! :shock: other than hay, the only mess he would make was peeing on the dogs bed when I let him have run of the room.
My 2 current buns however had to be contained unless I could watch they're every move (and even then extra measures had to be take to protect wires and tv remotes! :lol: I lined the pen with lino so had no issues with distruction whilst in their pen. The problem then was noise. I was woken early every morning to them having mad hours (sometimes I had to resort to food to quieten them down! :roll::lol
I did love having them inside though. I got to spend a lot more time with them and felt I had a stronger bond with each of them, especially Joey who had lived outside all of his life and got to spend his last 3 months inside being spoilt rotten
I hope you get to bring Fluffy inside, I don't think you (and hopefully your parents) will regret it, even if he does cause a bit of damge :lol: