If you browse the forum, there are lots of threads about how to reduce the amount of ventilation of a screen top to maintain humidity levels. IMHO, the easiest and safest is to use aluminum foil, because you can cover the entire thing except for where the lamp is and the lamp fixture can't burn or melt the foil if it is in contact with it. You'll lose humidity through any remaining surface area that is just screen, including where the lamp is, so you have to minimize that as best you can.

Don't be discouraged, even though people will be telling you to just ditch the tank. It really isn't that complicated to insulate it and modify the lid (even just covering it with foil) to retain humidity better, and basically once you get it all figured out you'll be good to go and you won't have to worry about it any more.

You might need to make adjustments come summer depending on the temp and humidity in your house.

Regardless, thermostats are important even though they don't come in the "starter kit". Under tank heaters can easily overheat because they are covered with substrate, which functions as an insulator. The heater stuck under a tank and buried in substrate can get way, way hotter than it would ever get if it were just sitting out on the table, and snakes can burrow or shove substrate aside and come in contact with that hot surface even if the top of the substrate isn't that warm. Even the snake's body can have an insulating effect. Thermostats cut the power when the set temp is reached so the heater doesn't overheat even if it is well insulated.