Thats only 140F, normal operational temp. depending on what youre running.
Thermal shutdown is 70+ higher than that.
As for keyboard covers, not recommended
Apple additionally now recommends against using these keyboard covers on current Macbooks:
The keys without covers already transfer to a small degree finger oil to the LCD screen of the Air, even the thinnest keyboard covers place pressure on the LCD, however normally this would have no bearing unless stowed away in a pack with pressure, nevertheless causing dirt and oils is increased with covers to transfer more to the LCD, ....Macbook Air as well.
Beware of keyboard covers and using same
Beware of using thick keyboard covers on your Macbook, some pretty ones sold online are rather thick and upon closing your monitor, touch the screen and transfer more finger/hand oil to the LCD but at worst press excessively on the LCD display, especially in the case of the Air and newest Macbook Pro Retina. There is ultimately very little purposeful use of these keyboard covers if you keep your hands clean, additionally they do not protect against spills as many people presume they do; directly yes, but at the edges no. They also making typing a more challenging experience and run a fine line between 'serves no purpose' and 'possibly damaging'.
Screen covers protect against nothing and place an unwanted layer between the LCD and viewing, additionally if you dont touch same or dont have any pets that might claw at the screen there is no logical reason to have a screen shield.
dust will accumulate regardless. Realistically what are you trying to protect the screen from. The back is solid aluminum alloy, the front LCD viewing screen should never be intentionally touched.
outside of a sneeze or some debris which an extremely lightly damp cloth can remove, all else is dust. ...
Use a soft paintbrush or makeup brush for cleaning
One very useful tool for cleaning dust from the LCD screen, the hinge area of your notebook and around the keyboard, is a very soft inexpensive small paintbrush or a makeup brush. The less you wipe your LCD screen with anything like a cloth, the better. This small brush is very handy, quick, and ideal for removing dust from around and on your notebook.
Small soft makeup brush or paintbrush for removing dust from the keyboard, hinge, and LCD display