Some kind of mini heat pads to wrap around the ALs could probably work, as long as they can withstand a bit of moisture. They have battery powered heated gloves, and wrist warmers, etc. Basically, you could just pull the power pack and heatedwire out of them, and then wrap that around the AL. Use a small transformer instead of batteries to power them.
Water proof LED strips are pretty cheap, and use low voltages. They make a good amount of heat. That's probably what I would end up using. 12v LED strips in the silicone ip67 channels or ip68, with the ends all siliconed up. You only need maybe a few feet or less for each strand. It will look like you're growing a little Christmas tree with lighted ornaments, but keep the medium in the layers warm for sure, lol.