Polycarbonate panels: I'm aware of them as an option, but I resent the shit out of them because they actually do much less effective light transmission than glass. EVEN THOUGH I agree that they would be less D: to transport.

Window opening: the reason I want that for greenhouses is that fundamentally they get very warm, and very steamy, so they need windows open appropriately to allow air circulation and to prevent your plants from... actually steaming themselves!

Polytunnels: I'm a bit D: D: D: about them blocking light and being less warm and Awkward To Anchor, but... maaaaaaaaaaybe?

(Will probably be late-notice prodding about moral support -- I work out when/if i'm having a GP appt on Monday morning.)