Yes,I've built one and find 32mm perfectly adequate.

If you let me have your email address I'll send you a photo of it as I can't seem to add it here. ( haven't a clue !) I can give you some more info too if you'd like.

I have never built one using 32mm water pipe but the galvanized tubing that is used is usually only 25mm so I agree with hank. The last post that you left I left a you tube link that the guy built is own tunnel and is very good in fact all his vids about is allotment are good for allotment novices like ourselves love his later idea regarding kids paddling pools

Thanks Steve and Hank, yes I've subscribed to his channel, its all full of great ideas.

Hank, just to say I've messaged you with my e mail address. Thanks again both for taking the time to answer.

John