An easy thing to do to create humidity is get a small reptile undertank heating pad from any petstore chain.. Petland or Petsmart or anywhere like that, they're like $10. Find a shallow heat proof dish.. like a shallow casserole dish or plate. Place the dish on top of the heating pad and fill with water. It creates quite a bit of humidity. You could probably find some regular heating pads at walmart or something too. Just a thought. Remember though, as your humidity rises so will your temperature in such a small space.. I would say your temperature will be the first thing you gotta worry about though. The humidity probably isn't going to hurt the plants nearly as much as heat stress would.
As BudTinsley stated, you could put plexiglass between your lights and the plants and pull air out of that space to reduce the heat. I've heard that plexiglass can lower temperatures but I've also read in a lot of places that plexiglass between your lights and plants degrades the light quality to your plants in some way. I can't say whether it is worth it to reduce the heat or not though. It's something that requires a little more research I guess.
It looks good so far though. Our plants are pretty close in size, I'm about a week or so behind you I think. Your plants definitely look a big healthier though, I think mine are recovering from my overwatering the first week or so. Keep it up man!