Thats a small area to maintain, I use several cool mist humidifiers in my rooms and the rel h. stays a healthy 60-80 % in such a small area one of the misters i use might work on a lower setting. One thing that i have control over and you may not is WHERE in the house my grow rooms are, the seedlings and clones stay in the basement which is separately heated, meaning its not part of my homes hvac system, so i have more control. If you are fighting your homes hvac system there might be issues with humidity. but you can seal off the tent from the vents, or simply turn the thermostat down, that will limit the effect of your homes heating system to draw moisture out of the indoor air. also 6 inch exhaust fan for a 4 x 4 might be needed when the plants are reeking but if not totally necessary for odor control you might consider restricting the exhaust a bit, I cap of part of the inlet side, the end that is drawing air, with a small peice of heavy duty aluminum foil so the area is reduce to about 50% if i cant slow down the exhaust by any other means.