Funny, I have some dwarf monitors in a tank as a growout enclosure with about 4-6sq inches of ventilation and have had none of the problems you describe. And they have a much higher metabolism than a ball python. most of the tubs I keep my pythons in only have a couple square inches of vent holes by the time you add them all up and I haven't had any issues yet. You are overlooking the fact that screen tops do not fit tightly, and I have yet to see a commonly available incandecent fixture that does not have vent holes in it. By the time this is in place the air moving through the fixture and coming in through the gaps around and under the top will be enough to keep a ball python healthy and happy. Oh, and my background has been the keeping of reptiles and most other manner of small animals for almost 20 years now. So I've managed in that time to make a lot of mistakes and learn from them. I only relate what I have found to work best for me, based on my experience.
To the Op: If by a brooder you mean the fixtures commonly sold for poultry, it will work fine if you have the room for it. They tend to be larger than other fixtures. I have one of those myself for use with a ceramic heat emitter in case I need extra heat
somewhere. As for helping the tank to hold heat better, you could get some insulation foam from a local home inprovement center and insulate the back and both ends. 1/4"-1/2" should be fine. And if you don't want to stare at bright pink or blue foam you could easily paint it witha foam safe paint before putting it on the tank. Acrylic latex works well.
Now if I were setting this up myself, I would cut a piece of plywood to fit the top, make an area for ventilation about 2"x12" with a way to cover part of it if needed. I would paint and seal the wood, then install a fixture with a CHE on the inside. make a wire cage to cover it, setup a thermostat. It could easily incorporate the light you are using as well. Once this is in place, you just set the T-stat for your desired ambient temp and adjuet the vent to kaintain proper humidity.