First you just need to put the heat tape under the cage you do not need to attatch it. If you wish to attatch it you would need to use a product like this. tape
Yes you do need a thermostat for heat tape.reason for a thermosat
Now you could buy a dimmer and a digital thermometer at Radio Shack. It is up to personal preference which method you want to use. I like useing a thermostat and a digital thermometer just to verify that the temps are what the thermostat reads.