Heat cable can be taped to the bottom or sides of tanks in a series of loops. If the cable is on the bottom, then the tank needs to be set on small spacers so it does not compress the cable.
Might also be a good idea to put a foil-based insulation over the cable as well, especially if its on the side. I know you have insulation in the UK that looks like bubble-wrap covered in foil, that stuff is great.
If it were me I'd tape down some expanded PVC to the tank and then tape the cable to the PVC. It will help spread out the heat.
Rope light is a series of tungsten bulbs in a flexible PVC tube. Here is a picture of some boaphile cages heated with rope light. They also come in red or blue for night time heat.

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Current snakes:
0.1 Gonyosoma oxycephala - (Silver/Yellow)
1.2 Gonyosoma oxycephala - (Green)
7.6 Gonyosoma janseni - (Black)
0.1 Gonyosoma janseni - (Black & Tan)