I think you need a 'whole house' humidifier, not because you are humidifying a house, but because you need it running all the time. I bought a five gallon evaporative one, with two tanks. If I fill it on Friday at close, it still is running and has water in it on Monday. I have it set for 45% relative humidity. My print shop studio is 15' x 15' x 12'.
Although it has only been a few weeks, and it is too soon to tell. I haven't had a single line drop out in the time it has been running. Every nozzle check print at the start of day used to be a fear and loathing experience till now.