Heat pads are very inefficient when used on the side of an enclosure. What has worked for me is to cover the whole top with wrap (can tape to top edges) and then place the dome (unplugged and cool) on top of saran in your area of preference and at least 1 in. from edges. Then using a sharpie; mark around dome's perimeter and use scissors to cut around circle but make hole 1 in. larger and you are done.

The one in. gap will prevent saran wrap melting from lamps heat and the increased coverage and sealing should help keep humidity with a couple (AM & PM) daily sprayings. You might consider getting an automatic (thermostat) or manual (rheostat) controller prior to Winter to help you dial in the correct temps; good luck !