Getting extra ventilation in glass will be tricky since you need to drill the glass and it will likely brake.
Mostly ventilation in the front in glass enclosures is done like this:
or the more fancy solution:
What are the night temperatures in your house during the winter? Chameleons do well on a drop in temperature at night so odds are you don't need to heat him extra. Íf you need to heat him at night better not use a red lamp but a ceramic lamp since chameleons will be able to see the red light with their parietal eye (3rd eye on top of their head) which will disturb his sleep and will cause health issues over time.
Drainage will be an issue, you'll need to find a way to collect the water you spray without having the risk of your cham drowning.
If it were me I'd probably take out the bottom glass plate, then build a wooden frame to fit the terrarium of 15~20 cm high where I can fit ventilation and a drainage hole with a piece of garden hose. Make the wood watertight with a couple of layers epoxy or yacht varnish. But I like being creative