Pebble Trays to keep humidity up?

Well I have lots of cuttings going now: Star Jasmine, Begonias, Buddleia, Physocarpus, Michelia, Hydrangea, Honeysuckle, Callistemon, Roses, Rhamnus, Cestrum, Brugmansia and a few more. Its been not quite two weeks for some things and less for others. Everything is looking good, for the most part. We had some cool wet weather and I think that was helping everything but the last couple of days have been warm and dry. Now the Hydrangea and Brug leaves are really wilting. I am misting as often I can, a few times a day.

I was wondering if putting them on trays of pebbles and water would help?

Yes. Pebble trays are a better idea. Misting is pretty useless for humidity. You'd have to mist every 5-10 minutes 24/7 for it to work. You're better off using a humidifier if needed.

Well I was at Orchard Supply earlier and I found these plastic humidity domes. They fit perfectly over the rectangular nursery flats and have vents you can adjust. They are taller than ones you seed to start seeds. I kinda felt stupid paying 8 bucks for a piece of plastic though so I only bought two. I am hoping if I am careful with them I can get many re-uses out of them!

Milk and water jugs with the bottom cut out work great. I use them all summer and winter covering 1 gal pots of cuttings, seeds, etc. In the shade in the summer. I leave the cap on most of the time. When you remove the cap do check very often for wilting. If it wilts recap for a few more days. Then I leave the jug on until good growth starts. Then you let grow in pot until it needs a new home. This method works with most plants. I also use 16 oz stryro cups and use a 2 litre drink bottle for a dome.