I'm not trying to be a jerk but under heat is the best heat source and I always strongly advise against lamps. I'm not even a fan of back heat in racking systems. You really do need a way to regulate your UTH, I've stopped pushing people to buy herpstats and VE systems but you can get a inkbird controller on amazon for like $40, it sounds like it might solve your heat issues.

Sent from my SM-G920W8 using Tapatalk