My tunnel, has been mostly 'open', like manic scousers I have screenmeshing on the doors, since the fear of frosts (hard ones) passed...I close it up if it turns chilly in the day (mines in the garden too) to get the heat up a little for the overnight temp to be a little better. The min/max temp guage is vital in my opinion, I try to keep the tunnel between 60 and 80 in the day, which has resulted in having shade netting and shading blinds put on, they are staying on now as well because the plants all seem MUCH happier with their environment and the ground isn't drying out so fast.
Mine is in full sun all day (when there is any) and temps have rocketed off the scale on one or two days where I haven't opened enough vents...
It looks like this...26x12ft
http://nomspatch.blogspot.co.uk/p/the-polytunnel.htmlshading looks like this...
http://nomspatch.blogspot.co.uk/2013/06/blazing-junewell-it-was.htmlI hope this helps a little, though I admit I am still learning how to manage it properly (its been up for 4yrs now (ish) terrible memory for dates me!) but I couldn't imagine being without it now...