Hey bud, sorry for the long silence, was on vacation with the fam for a week or so and committed to putting the phone/computer away.
So to answer your question I feel like this is basically an ongoing evolution. I had been running the small oil filled heater in the veg tent but it finally kicked over the summer and I’ve just been letting things deal with no heat assistance since, but I’m still kinda shopping around for the next solution. For the 3x3 I’m still using the terrarium heaters with the ceramic bulbs hung from the ceiling. I don’t love how this kinda neglects the necessary heat at the root zone but it works for the limited space I have running two earth boxes in a 3x3 and the plants seem happy, so I’m letting it ride. I have/had both heaters connected to inkbirds to kick em on/off when needed. Until I identify a better way across the board this is how I’m limping down the road. Hope that helps, and hope the discussion continues here. One thing about all aspects of growing, even room design, is nothing ever seems to be final 
