[Amilo]

Has anyone ever fitted a auto-window opener to a poly_tunnel? is how did you do it?

[Fen]

Not sure that the structure would be rigid enough. In a greenhouse the auto opener is fitted to a rigid base and as it expands the window end gives and it opens, In the side of a polytunnel the frame might just be pushed down and the window remain shut.
Have you thought of an auto opener fixed to an end sliding door?  Or even one at top and another on the bottom. If door frame is solid timber door should be pushed open as temp. rises. No gravity involved so you'll have to shut it youself.

[Trillium]

I know the openers that are sold here always clearly state that you need a rigid frame to compensate for the pressure involved of pushing open the window or whatever. I plan to get one for my cold frame system (don't have a greenhouse or polytunnel).

[Amilo]

I was thinking of fitting 2 of them to the wooden doors at each end, but its all in the planning stage at the moment, my last tunnel got blown down a few years ago and I have a supper duper home made one on the planning board for the end of this summer.