Yo Priznn. The fan on my little space heater was not powerful enough to duct its output. I used an old 6" centrifugal fan on a speed controller to give it a little help. I then used 6" flex duct to pump the heat into the tent.
I also have an 8x8 tent I have heated up before. I know it could get over 100F with 4x600s and no AC during the winter. You might need to experiment with the right number of lights, heaters, and fans to get up to 120 and hold it for an hour.
It took me a couple tries to get something rigged up that can superheat the space consistently, but now it's really easy. I'm going to give my third heat treatment today and I should be able to pull my current crop through to harvest.
I just finished up the Cherry Pie in my last grow. Definitely some sweet smoke. Good luck man!
Yes, it takes some trial & error to get temps dialed in, but once you get it, it becomes simple. Just turn the heat on once a week or so if you still have mites coming into your room from outside, or from your environment,ducting, etc.
Just don't have fans blowing hot air directly on plants, as that may burn them a bit. That's another reason to raise your plants off the floor as much as possible. You can have your fan blowing air under the plants to get circulation. I use milk crates, upside down pots, cinder blocks and boards, or a table...anything to raise plants off the floor, as heat rises, and the coldest temps will be on the floor.
When you start over, scope plants carefully DAILY, and continue to scope throughout grow, because these mites have a way of coming back. And start your plants with aspirin from the get go, as this mitigates the poison the mites inject if more get in the room. Even a small number of mites can damage plants due to the poison. Damage is not caused by these microscopic devils by eating the plant. They are too small to consume much, but their poison is nasty and lingers.
A good scope is your best friend when dealing with these tiny monsters.