Yeah, your description of our recent weather is just what I've been seeing too.
I've not had a Botrytis problem but I've had trouble because they were staying too wet, even for humid loving Masdies. I had had to leave them outside while someone fitted power in my greenhouse and it was wet wet wet that day and I was already worried they had stayed wet too long before that. A simple plain ordinary fan for a couple of hours each day got them dry enough that by this morning they needed watering again... and then today was much brigher and sunnier anyway.
As it has been nice i have been able to open up the greenhouse in the day which has got rid of the condensation ,but as soon as it is closed for long periods the condensation comes back with a vengeance.Something i could do with resolving ,as i have already said i think a large extractor fan could do the trick ,but i am not sure .I already have 5 fans running 24/7 so adding more of these even though will only do good ,don't think will do the trick.