Hi John
I have a 14 foot by 45 foot poly tunnel with 7 foot double doors at both ends. It does get hot in Summer and I do water things like beetroot and tomatoes twice a day if they are wilting.
I have not employed methods like sinking plastic containers in the beds to seep out water slowly but thinking about it I might try that next year.
I love my poly tunnel. I have had it 15 years.