Den,
We have a mister for our Conventional Kiln. Use hot soft water to keep the tips from plugging. The biggest problem with water mister is it takes a huge amount of additional heat to ramp the RH fast enough to do any good.
I think a DH kiln would need an additional heat source to keep the temp up during the conditioning step.
Also, the higher the kiln temp during the conditioning step the better it will work. 120 degrees is fairly low.
A steam generator if sized right would work better.