I recently purchased the JB Wholesale xpen (I thought it would be a good way to ease Gossy into having the run of the house when I'm gone) and was a bit disappointed. I only ordered the 36 inch one and the free shipping doesn't apply JSYK. What I was really disappointed in was the latches on the door - they are not at all secure. It was really easy to push against the door a couple of times and they come free.
Are you sure the xpen is right side up? There is a name plate that should be at the top of one of the panels, if it is setup upside down then the door latches will not work correctly and will open really easily. I have several of them and all the doors are just as secure as all the midwest pens I've used. I've never had to worry about the door, I don't think there is any way Piper could open them.
I'm sorry your not happy with it and I feel really bad since I recommended it. Also I never got charged an oversize fee just standard shipping, whereas most places charge extra for xpens and crates, but maybe they changed that recently.