Claustrophobic Cats

Dave the cat doesn't go outside because he is an old man and he has a nasty skin condition on his paws. After months of antibiotics and various procedures we have finally got his paws to heal, but they will away be at risk of breaking down again so we have to be careful with him. He is very much part of the family now and he likes to be fussed and stroked, but only on his terms, if he is not interested he will make his feelings abundantly clear. He gets on very well with Robbie and recently he seems to be taking on some of Robbie's traits - they both share a passion for food! Robbie made all that fuss about being claustrophobic a few weeks ago and now it seems that Dave has decided that he is claustrophobic too. He has the enclosed type of cat loo and has always been a very clean cat but several weeks ago we noticed that he kept using his tail or his head to hold the door open while he 'did the deed'. Then we had a couple of mishaps and it was clear that he was trying to avoid going inside. I decided to provide him with a basic cat tray instead, and he is much happier with that. There is just one problem, our other cat Oreo thinks it is the ideal place to sleep! Why is life so complicated?