My shop is a converted pole barn, I built trusses in place and removed interior poles before pouring the slab - The tin roof was replaced with CDX (NOT 'Overly ****** Board), tar paper and 3-tab to match the house. (Added bonus - I now have to open the doors and look outside to know if it's raining)
It's essentially unheated and is (so far) uninsulated. My "anti-rust" battle consists of the Johnson's on all cast iron surfaces, breathable dust covers, and the clamp lights I mentioned earlier - jointer(s) , a cast iron router table, milling machine, band saw(s) ALL get clamp lamps with mostly 100 watt (rough service grade) incandescents, some powered by speed controls (since it doesn't take a LOT to keep above dew point on a localized area) - long tables get TWO lamps, placed approximately on thirds.
All nicer/more delicate accessories reside in a dead 30 cu. ft. upright freezer, with an "outhouse" lamp socket in the bottom (another speed control takes the 100 watts down to about 30, keeps the inside temp around 75 in winter.)
NOTHING ever rusts in that (added a small vent on top)
Humidity isn't that low in this part of Oregon, but so far the worst I've seen is uncovering the PM66 after about 6 months of non-use, and finding 1 or 2 fingerprint size minor rust spots, easily buffed out with gray scotchbrite.
I attribute those results to the combination of the lamps keeping surfaces ABOVE dew point so they don't condense, a BREATHABLE cover to let any small vapors ESCAPE, and of course the wax.
After the first minor rust I made sure to do TWO coats of wax; problem has NOT happened a second time... Steve
Edit - Sorry Jrad, missed your Q - "
Johnson paste wax INGREDIENTS: Deodorized Naptha, Carnauba
Wax, Microcrystalline Wax, Paraffin"