There are a lot of options for heating cages. Heating methods depend on a number of factors including the ambient temperature of your room and your cage design.
To prevent burns, any heater should have a digital thermostat to control temperatures.
Your standard aquarium with a screen lid is not going to hold in any heat. You generally need to heat the room an aquarium is to the low to mid 70s F. A heat pad on a portion of the bottom of the cage can be used to create a hot spot/"basking spot" the snake can use to warm itself up. Place the temperature probe of the thermostat between the bottom of the cage and the heat pad, and make sure to leave an air gap under the tank.
If you cannot heat the room then adding a heat source to the top, like a CHE, can be done to raise the ambient temperature of the tank. However, adding a heat source to the top of such a setup, say off to one side, is an excellent way to prepare jerky. I'm exaggerating a little, but you do need to be careful adding heat sources at the top of aquariums because it can create a convection setup that dehydrates the interior. Water bowls placed under the heat source, deep substrate that is kept moist at depth, humid hides, etc can mitigate the dehydrating affects of the heat source. Also, setting the thermostat to only heat the air to the mid 70s can help as well.
Closed enclosures trap heat much better and give you a little flexibility. I would lump rack systems and PVC enclosures together as closed enclosures. You can also add a solid top to an aquarium with minimal ventilation holes to seal in the heat. Sometimes belly heat provided by a heat pad is adequate for such setups. Radiant heat panels can be used to raise temperatures and are very efficient. Heat cable can be wrapped around perches to provide basking spots. Something as simple as a LED bulb in an enclosed fixture can raise temperatures a couple degrees.
