Most, if not all, frames have some method of anchoring them to the ground. It may be holes drilled in the bottom edges of the frame or pegs over the botttom edge. Our glass frames sit on a base made of 3" square timber and are screwed down to this - never moved even in the most viscious gales. Actually, our cheap plastic one jus sits on the ground in a sheltered spot with no fastening and it has not moved. I do lay some heavy pieces of wood on top of the plastic one though, when the wind is strong.

We don't normally have very high winds here, and we have still lost our little plastic greenhouse - damaged irretrievably - and that was on flagstones, but tied down with guy ropes and VERY robust tentpegs. I'd go for something that you can screw down!

Thanks to both of you-I will try attaching it to a timber base-do you mean that it wasn't fixed to the floor but the weight of the timber base made it heavy enough to withstand high winds?

Exactly whay I meant, Sparky ;-))