Kenny, Try adding a little peat--it helps retain moisture. I always add it and my soil never gets crusty on top. I mix about 1 part peat to 3 parts potting soil. You should be able to find small bags of it at Wal Mart.
The brand's schultz, 'made and manufactured in canada' It doesn't crust anymore now that it's in the small heated greenhouse thingy, I used to just mist lightly, turns out I need more water thanks everyone!