I was also worried about that, but for this PC its only sun that can melt it haha. But yeah it would be better to print with petg or abs
Cpu temp never goes above 45C lol. Usually at 35 and case fans are not even spinning. Also mbo is "raised" 10 mm from back wall if that make sense.
I printed a case for a small PC that I user as a home server 3 years ago, and I used the cheapest PLA out there. No warping, nothing broke. It is cooled by a single 80mm.
As long as there's enough airflow to prevent the PLA from actually heating up, it will be fine.
I've also had problems with PLA prints delaminating and becoming brittle over time, especially if it's being flexed or exposed to sunlight. Some PLA's are worse than others with this, though.
I use PETG for anything I want to last a long time.
If you're willing to get into annealing, I've had good service from annealed HTPLA in high temperature/humidity and even overpressure environments. I'm three years into a build that gets multiple hours of use in such conditions a week and it's held up fine. There have been other problems, but nothing related to bad behaviour out of the HTPLA.