I have the Canterbury run too. My old one from P@H was sturdier but not folding so difficult to move around the lawn etc. I was a bit disappointed by the Canterbury, it uses basically thick wire rather than welded metal grids, so probably wouldn't survive my son's footballing as the old one did. Like Betsy, I find it difficult to get the sides to stay straight, and have the lid resting on top as screwing it down would render the run non-folding.
I was trying to find folding hinges that would hold the sides in position when open but couldn't find any. However I just had an idea - when I'm getting it ready in the spring, I'm going to buy some hooks - the straight sided ones which I think are for mugs - and screw them into the verticals, then use a long piece of wood resting on the hooks to hold the sides in line. This might help you too
@Eddie & Elvis ? Though possibly your lawn is just a bit too sloping, but it's worth trying.