Watertight

I bought some more poly yesterday and filled in the holes in the ends of the "greentent". It started to rain while I was working, and, amazingly, even though there is a seam right in the middle, with no continuous run of tape, it wasn't leaking inside! It was cozy and rather watertight! I plan to reinforce the top with another strip of plastic, and then it won't leak for sure. Unless it just blows away (still a possibility.) I was distressed to see a warning on the bag that the poly came in - that it shouldn't be used in the sun. Why was *this* not mentioned in any of the "build your own greenhouse" sites?
We are promised some decent weather later this week, so I plan to move everything into the greentent this afternoon when I get home from work. I want to make a high shelf at the north side, and a low one at the south. They're calling for frost again tonight, but inside the greentent things should be safe.
Strawberries, tatties, and all the other started plants - I'll probably leave the ones in the mini greenhouse right inside the greentent until things stabilize.
I was shocked to see on Robin McKinley's blog that she was expecting frost last night in the UK. Whatever is going on? Can it be the Icelandic ash again?