There is nothing wrong with your guitar. It's not the humidity, or the case (lol, that's a new one), or the truss rod, or the tuners. You are not installing your strings correctly. If your luthier did not explain this to you, I would question his experience no doubt. The problem is a combination of things. Once you understand these and compensate for them, your guitar will stay in tune. First as stated, you must lube the nut(pencil shavings work fine for this). Second, you must lock the string around the post (you tube will show you how). Third, use as little wraps around the tuning post as possible. Fourth, Ernie Ball makes strings that are reinforced at the ball end to prevent the wrap slippage at the stop bar. These are the best strings i have ever used, and assist in helping the guitar achieve rock solid tuning stability. Finally, adjust your intonation AFTER you have stretched your strings. As any string stretches, the intonation changes. You need to make sure your strings are fully stretched or your intonation will be off and you wont play in tune. My les Paul rarely drops out of tune. As a matter of fact, it stays in tune better than my Floyd rose Guitars. I have ZERO tuning issues because I have followed the steps above. Hope you read this, because I know it will help you.