Hi John,
Looks like sun scorch alright. I get it on my toms when I move them out from the Growlights to direct sunlight.
It wont really do any harm in my experience.
As for the Temperature issue. Toms need reasonably even temperatures – day and night, by which I mean there should ideally not be a big drop at night over daytime temperature. Difficult thing to control but can be done. Have you considered modifying the Pollytunnel and using one of those automatic openers they use in Greenhouses?
I’m sure Charles will have a good idea of how best to tackle this problem.
Don.