That's what I was thinking. I had a similar problem, my 41qt rack was constantly showing condensation on the right side of the tub this summer. I have never had problems with humidity living in AZ or WI so I've never purchased a hydrometer. I decided it was time to after seeing that.
Walmart has nice and simple Accurite ones for around $10 and soldering irons are a little less than that. My tub was showing around 75-80%, so I added another row of ventilation holes. Now it is perfect like my other racks. If it is in fact really that high I would purchase a soldering iron and make some more ventilation.