akdave If you get the chance can you post a few pictures of your set up? It sounds interesting, I really like the idea of the fan going over the surface of the water. Check out this video https://meatgistics.waltonsinc.com/topic/1099/cured-sausage-205-advanced-thermal-processing for an idea to raise your relative humidity, even more, I think the sponges, in combination of the fan, could make a huge difference.
I might do some testing here with a fan now, what make and model fan did you use?