My woodworking shed is insulated, sealed good enough and controlled temp year round, with an elevated joist floor.
But my welding shed is not sealed and not controlled currently with a dirt floor. Moisture in there is a real issue weekly. I go with a multi approach to combat rust. I spray all steel with CRC 3-36 and have a box fan blowing constantly to circulate air. I think CRC 3-36 is much better than WD-40 and other products. I've seen thick condensation on steel parts, welding tables, drill press chucks, etc. and once that water evaporates, no rust. CRC provides an excellent barrier. Without that fan, evaporation takes so much longer on the large temp and humidity swings here in middle TN.
I'm slowly sealing in the welding shed, adding recycled denim insulation that comes in weekly food delivery boxes, a pile 6 ft high now. A few months and I'll have enough to do the whole shed. Then put up OSB sheets on the walls. Cheap, simple, and can get dirty from metal grinding. Lastly will be to put in a floor that seals out wicking moisture from the ground, but I don't want concrete. Just too tiring to stand on for long days.