Hi Can anyone recommend a dog pen that I can easily attach to a crate? By this I mean that the first and last panels will clip onto the door side of the crate so that the crate door opens into the pen rather than straight into the room. I'd like to start leaving my pup semi-confined more often, i.e. not in his crate, but not with free roam of the room either. But I'd like him to have the option of going into his crate as well, without just putting the crate inside the pen, which will just waste space in there. Thanks!