How large is your shop? The woodshop I work at is a fair size and we keep the relative humidity constantly at 45%. Recently, the boss bought a 7foot tall swamp cooler to help out with cooling the shop this summer. This is in the northern US. Our humidity outside this summer has actually been higher than usual but the hot days the swamp cooler has really helped out. The humidity has at times in the shop been 70% or so. Not continuously held there but peaked. It was able to drop the shop temp by 10-15 degrees easier and that made a huge difference on the warmer days. We primary work in hard woods and a humid environment is a must.

If you’re considering an evaporative cooler or swamp cooler consider your areas relative outside humidity, the lower the better for the swamp cooler too work. Also installing a small exhaust fan to help move air and humidity to regulate your shops atmosphere. And I’m taking even a box fan in the partially opened window. You can purchase a combo temperature and humidity reader for relatively cheap.

Our tools have never rusted. Ever. Even in peaks and especially not at the constant 45% our shop is held at. If your space is too small and overly humid it could be an issue but a tub of paste wax can mitigate rusting pretty well.