A quick update in case anyone is in a similar predicament… we did as @Acciovacation suggested and waited until the morning of to buy our tickets and weather turned out much better than expected. There were a few rain showers (including a heavier, slightly longer one mid-afternoon that seemed to clear out the crowds a bit) but no thunderstorms and even blue sky sometimes! The weather even helped us take two rides on Krakatau with a 15 minute wait - one about 45 minutes after park opening and another right after the rain ended.
I found advice about shaded seating in this old post: https://forum.touringplans.com/t/info-for-shade-lovers-at-vb/95278/22 When we arrived, we walked by all the seating on the map (crowds seemed quite light when we arrived at 9am so we had lots of options - though the smaller shade structures were all taken). We ended up sitting in the center of the middle shade structure at the entrance to the Fearless River at the back of the park. When the heavy rain moved through, we noticed that the middle row of chairs where we were sitting were the only ones to stay completely dry.
This spot worked out really well. We had convenient access to so many slides. We were a big family group and easily divided up and met back at this spot without our phones. Plus, various configurations of family members took many laps around the Fearless River because of the location. And, if any family members were on a multiple lap trip, any others who wanted to join could easily spot them and hop in for another ride around the river!
We actually never did the wave pool at the front of the park because everything we wanted could be accessed from this central spot in the back. We were never too far from restrooms / our locker or any of the slides. (Including being able to pop over to Kraketau right after the rain). Also, perhaps due to the potential for bad weather (and/or maybe because it was a Volcano Bay Nights event that day), we never waited more than 10-15 minutes for any slide and most slides were a walk on. The longest wait of the day was for the bus back to the parking garage - and even that wasn’t too bad!
So, nearly 3 years later, many thanks to @darkmite2 and @bebe80 and @ruthie2780 for that original detailed post!
Some photos:
We sat under the middle shade structure at the entrance to the Fearless River (marked by a black star)
Shade structures at the entrance to the Fearless River (middle one is on the left)
View from our seats under the middle shade structure
Volcano Bay from the front as we were leaving at the end of the day - with blue skies peeking out!