I think that would be a really cool thing to do! Just get a cabinet with doors and windows from WalMart or Canadian Tire (Crappy Tire for us Canucks) or wherever, and then you'd need a humidifier/dehumidifier hooked up to it. I would think that you'd need just a little bitty one, since the normal sized ones are designed to humidify/dehumidify entire rooms and that'd probably harm your guitars.

Then all you'd need are some hook-type things to hold up the guitars... I've seen them for sale at guitar shops; it's actually what they use in music stores to hold up the guitars on the wall... I'm sure you know what I'm talking about.

I think it would be a fun little project with much usefulness! Let us know what you think/how it goes!