I have finished willow's playpen! In the end I used a piece of old carpet to be the base and gaffa taped it with about half a mile of gaffa tape so that it joins seamlessly to the cardboard bottom flaps and there are no airholes at all. Willow was happy for..... An hour and a half
as long as I stayed with her so she could use me as part of the game. V relieved altho I am.sure she will find a way to destroy the corners at some point. I just used the carpet as a temp measure because it was there and can't spend any more on hamster funds right now!