Use a deep pan, filled with water, with a spare small aquarium heater in it, and set the bottles in that. Then the temperature should be eliminated as a problem. To find any leaks, get a bottle of children's bubble wand liquid. Drip some of it at every single joint of any kind in the CO2 system. Wait several minutes, then look for a small mass of tiny bubbles at one or more of those possible leak sites. The leaks that are a big problem can be very, very small leaks.