im using similar system, i have 27gal heavy duty plastic tote and i can control fermentation temp of two 6.5gal carboys, i have it connected to my own design

cooling system and 150w aquarium heater, everything is controlled by stc1000 dual stage controller and its working very well. Till Sunday i was keeping it steady at 75 and now im cold crashing at 55 (im not sure it would go much lower), ambient is around 68F