Bob, I really feel your pain!
I have an old garage with a single-pitch sloping roof. Well it's now got two roofs as we had the old one covered with a new one. that stopped it leaking, and condensation forming on the inside of the roof, but it still gets really humid. In the autumn this is OK, but in the spring... warm moist air comes in to the cooler garage and immediately condenses.
If I take no action the rust is immediate and horrid. I've just been cleaning bandsaw, morticer and table saw tables for that reason (haven't done much work in there this year!). I have a tubular heater underneath the main tool chest, but it's inadequate going to double it up again for this coming winter.
BUT... the thing that does work really well is stopping the damp air getting to the metal in the first place. I have a cheap solution that does work really well. But you need to be consistent. When I first started to do this it worked excellently, even though the damp was far worse. I got complacent, hence this year's problem.
So my "cure" is really simple: bin bags, or pieces of them. Cut them up carefully so as to get a single large sheet of polythene. DO spray WD40 on first (or use Liberon mchine wax - it is brilliant) and wipe it into all the little places, then put the sheet on right next to the metal and if necessary weight it down (offcuts are excellent for this). For the bandsaw I can get a large bag over the top, and have simply cut a tear in a sheet that goes over the table (blade still attached. The bag comes down onto the sheet. The mortices has a single bag covering all (I have to take the handle off, but that takes seconds).
You increase the effect of the Liberon or WD40, too: the lighter oil fractions can't evaporate off so easily, and there's a healthy vapour pressure inside the bag or under the sheet, which stops water vapour from getting close to the metal surfaces.
On Liberon, it really is very good. I use it on a lot of surfaces that can't rust (e.g. the router table), and a little goes a long way, too. I've got three cans of it, the earliest bought about 8 years ago, and I still haven't quite used that one up (have used it to keep the other two runny, as it was more liquid than them). It has one odd, really useful, property: It seems to lift rust you can't see or clean off otherwise. I use it as a check that surfaces are clean enough: wiped on with a kitchen towel, any dirt or rust is obvious, so I go over again with an emery block and then clean with white spirit.
I bet you can get bin bags and WD40!
E.