Re shelter and open areas, so far in my riding experience on trips I've never been in that situation, but can see how that would be scary.

Re rain gear, I'm completely in the corner that believes that full rain gear makes all the difference, rain booties that rain pants go over mean your shoes aren't soaked, and a helmet cover means rain isn't pouring down your face and neck.
Sure if it's super hot out it's not a huge deal being wet, but I've ridden in rain and storms tons of times where it's 20c or less , 68f or less, and you get miserably cold fast--and I'm talking summer months, July August.

We still don't know where this person is, if they are in North America June, France, although I kind of assume somewhere in North America, but could be wrong.

But no matter, that's a drag for their first trip bike touring experience they have had bad luck with so much forecasted rain.

I know when I started out touring, I didn't have rain gear, just a jacket, and kind of hoped for the best.
Only got more gear as the unpleasant experiences added up over the years.