Hi,
You can insulate the outside of the tank with cork, polystyrene (sp? ), bubblewrap etc.
The bulb in the heatlamp can be changed to a red or blue one which will not disturb them and can be left on 24/7.
This will keep the ambient temps up and then your heat pad and thermostat can be used to provide the hot spot.
Check out some of the stickies and thy will show you how others have organised their setups.
dr del