Everything for my tub finally came in! I'm getting my lil bloop in a few days which is really exciting!!!!

In the meantime I'm adjusting my set up to have perfect husbandry and after a day everything is great except for my cold side temperature. My warm side is consistently 90 degrees, but my cold side is only around 77-78 degrees, which is lower than I'd like. How would I go about heating it? Could I set up some sort of insulation?

Bonus question: I'm using a 15 qt tub because I felt the 6 qt was way too cramped up. If I have crumpled up paper towels/newspaper/extra stuff in it, the extra space won't stress out the snake right?