Having a vapour barrier on the bottom sounds like good advice Zeedman. I found a paper from Purdue on managing the environment in high tunnels that says 'Many growers don’t seal all cracks and crevices, keeping their tunnels somewhat “leaky” or “drafty” to reduce relative humidity without having to open and close vents so frequently. Of course, leaky tunnels won’t be as warm, and if a heater is used it will cost more'. We have an option to place the tunnel at the end of our carport, and if we did that it may alleviate a lot of the excess moisture.
Once the weather gets above 15C(59F) at night time I am thinking of putting the tomatoes and peppers in the back of my husband's pick-up truck. We could park the truck in the carport overnight, and then just driving it out into the warm sunshine in the morning. That would be so easy! Then if the sun gets too hot midday-- drive it back into the carport. Stay tuned for further updates on that front.