Still smiling about that 'turtled tunnel' but I know what you mean.

We live on the side of a valley up a hill -pretty high altitude (I'm in cloud now) and the wnd 'prevails' both ways - which is very unfair!! It comes East west and west east depending on its mood! Luckily we located our tunnel east west with a door in each end (it s 24 foot) so its ok.

We didnt bury our plastic we used 'base rails' to hold it down with exhaust clamps (big FO lumps of concrete on the poles in the gorund mind you!) We haev been surprised that it has stayed put (fingers crossed)

Since we put our tunnel up three years ago we have helped put up a dozen or so with neighbours and I have to say that the burying plastic is harder work but feels 'good and solid'

One other thing I was thinking - I have had a problem with sil errosion which I dont think you would have wth the burrying method either. As I have the base rails - we found the water run off washed away the soil around the bottom of the tunnel - this could be:

a, because we are in Ireland and it rains a lot!
b, because we and the tunnel are on a hill.

We ended up putting boards and slates along the bottom edge to stop the soil falling out of the tunnel!