Polytunnel water collection

Some sort of frame to screw guttering onto?

Only way i could think of its to cut along the plasctic about 4ft above the ground level and add a a wood rail and gutter along under the cut and fix to the front of the wooden rail and the remainder of plastic back to a wooden rail that the guttering is fixed to

I know what i mean lol as we done the same type of thing to my Dads anderson shelter with roofing felt to save water on his plot. Its all held in place and seems to hold up against the strong winds we have had. 

We have filled about 3inch of water so far this year i know a tunnel would be lots bigger than our shed but if it dont rain you cant fill it.  The ground is so dry around these parts we are still having to water most days.

I like the sump idea. I was thinking along ataching a length of guttering along the side of the polytunnel  along with a stuck on plastic  flab to direct the water into the gutter then into our rather large water butt.