Humidity

My humidity never goes past 40 - 45% (low as 30% sometimes) with no real issues mate

 

Turn off the exhaust fan. Problem solved.
Your fighting an unwinnable battle as long as the exhaust fan is running. With the fast air exchange you'll never get more then a point or two over the outside-incoming air.

Humidify here can get down to single numbers and the plants don't care either way so my advice is not to get all worked up over it.

BNW

 

I've had to use two humidifiers before in a 3 x 3 ft tent to keep humidity above 60% in the winter.
Ultrasonic humidifiers, which are really foggers, can get humidity up higher than evaporative types.
Those blow already-humid air across wet wicks, but the already-humid air can't pick up much from the wicks.
But the ultrasonic (top fill is much more convenient) humidifiers don't disperse the fog very well, so I put a fan behind ultrasonic to blow fog around. Blowing fog directly on plants isn't good.

Humidity can usually be raised by lowering exhaust fan speed.

Growing with high humidity will produce bigger, faster growing plants.
Growing with low humidity still works, but the growth will be less.
But sometimes plants can get too big.

 

In that case you will be golden mate
As soon as you have watered posts and "eventually" plants in there, it will massively increase your humidity!
No drama

 

Your atmosphere will change as soon as you get those watered pots under your light mate - What lights u running? HPS / LED?

 

You can slow your fan speed down with a fan speed controller, real cheap. You can aslo partially recirculate some humidified air by placing the exhaust so that about a quarter of humidified air is sucked back up, but once you add plants you should be fine slowing the fan speed.

 

Sounds good to me... If I was you, I would get your pots watered and ready for seed... Put them in ur grow tent to warm up with lights/fans/exhaust all running and 24 hours later, check ur humidity /temps etc.
Then you will have a better idea of your "environment". Once seed pops ground and grows.. again, this will raise humidity!
You have nothing to worry about. All good fella.

 

My house stays at about 20% most of the winter and I've never had issues with too little humidity. You don't need your exhaust fan at this stage, just a small fan if your plants are in an enclosed space. Later when you do need your exhaust fan it will help keep your humidity down.