Some authorities assert that a mezuzah in a sealed glass case that does not come in contact with the wall and is not exposed to the elements does not need checking. However, the Shulchan Aruch and the later authorities do not mention any exceptions to the halachic requirement that an individual should check his mezuzot every three and a half years. As you wrote, extremes of heat and cold and exposure to sunlight can ruin even the best protected mezuzah.
Therefore, other authorities recommend that one should check all the mezuzot of his home at the prescribed intervals without exception.
 Shulchan Gavo’ah Y.D. 291; Halichos Shlomo, Tefillah, 4 (end).
 Agur B’Ohalecha 32:3-4.