Ya, I-25 sucks, but it's nothing compared to the West Coast freeways. Seattle is a nightmare anymore. Where are you at?
I just have a 2x4 veg tent, and an ~3.5 x 8 ft flower closet. I have one 6 inch fan sucking air outta my flower closet and outside. Another 6" just blowing back in the main room, and a 6" intake fan for that closet. Then I have a 4" intake and 4" exhaust for the veg tent.
Since I ran that one exhaust outside my humidity has dropped drastically, and I don't even need to use the expensive dehumidifier I bought anymore. It's actually a bit too low.
Also I did some research on the elevation thing. Not all of what I read applies to indoors, but the lower air pressure and lower CO2 makes sense. So does the lower RH. Outside the ground warms up slower at high altitude so that makes sense. But the Sun's stronger up here since there's less atmosphere so they should grow faster outside in that respect. Interesting. Here's one of the things I just read.
How Does Altitude Affect Plant Life?
sciencing.com