Bringing colder air from inside the house sounds like a better solution, also need to exhaust the tents air outside the garage so no hot air is added to the garage…
Or setting up some sort of permanent air extractor for the garage itself, so it won’t hold any hot air inside
I think you’re leaning the right direction using the larger tent as a lung room but the 4x4 is not large enough. When the house ac is only circulating 70 degree approx air all is good but when the ac is cooling that’s 45 to 50 degree air I would be concerned these cold temps swings could cause growth issues and possibly herm. A larger lung area will allow more stable temps. Also be sure all exhaust goes outside not recirculating.