When printing PLA you do not require an enclosure! PLA does not shrink as much as e.g. ABS. When printing PLA you should definitely ventilate your casing. I guess your steppers are also located in the enclosure, so you should be careful of not overheating the enclosure. Not only the steppers, but also think of the cold end cooling, too much heat in the enclosure means that the cold end cannot cool enough to prevent the filament to melt prematurely; this can lead to clogs. Also note that the printer electronics board may become too hot too (too hot stepper drivers will cause steppers to miss steps).

I once tried a towel over a Ultimaker 3 Extended to print a difficult filament to keep some heat in the enclosure; I encountered the above
problems when I was young(er) and inexperienced :) We learn by trial and error some times!

However, ABS, requires control over the temperature during printing. Draft or uneven temperatures may lead to problems related to layer separation or heat bed separation. Many of the high-end box printers have doors available to enclose the front, this results in an enclosure with an open top (sometimes even for the top there are covers available). The heat of the bed then heats up the enclosure. A constant temperature of 45°C should not be too high to cause problems. When boxing it up completely, you could use a temperature sensor to monitor the enclosure temperature and schedule a fan to ventilate when it gets too hot.