Sorry to hear about your tomatoes. I have given up growing them outdoors BUT if you can keep the leaves dry, with a cover as you suggest, then blight should be prevented from infecting plants. It only enters leaves and stems that are consistently wet, from about mid June when there is enough warmth. Good luck, let us know how it works!
PS you can compost the blighted leaves and stems (I do always – and indoor toms & potatoes are all blight free this year)), the spores do not carry over through soil or compost, only arrive in humid air.
