Aside from the already good advice, make sure you put epoxy on the shaft and down the hosel. Load it up down the hosel, in fact. Sure 95% of it will come oozing out, but at least you know that you have 99.9% coverage on both surfaces. Also, make sure the shaft and hosel are clean before you apply the glue. I use a q-tip and isopropyl alcohol and swab out the hosel until the q-tip comes out as white as when it went in. You can go through a dozen+ q-tips in the process, but they're cheap. Then I blast the hosel with compressed air to make sure that there is no junk in there, and to make sure the alcohol is fully evaporated. Then you can load up the shaft and hosel with epoxy, and make sure you get a good 50-50 mix and stir it well. Don't skimp on the epoxy when mixing it. If you're only making a small batch it's easier to wind up with a 40-60 mix.
Make sure to get inside of the ferrule fully coated as well. Keep a rag with solvent handy because there will be epoxy flying everywhere and it's easy to get it on the club. Let it cure in a low humidity, constant temperature area, even if it has to be your dining room. A damp basement or hot garage is not a great place to let your clubs dry. Also, I give my clubs longer than the stated curing time to dry, although that is probably more superstition than anything. If you do the above then I suspect you'll no longer have a problem.
I don't think the ambient humidity is going to have much effect on things, as the epoxy is solvent-based. But one thing I'd add is to remind stroh to load up the shaft and hosel with epoxy.
