Drill holes for ventilation at the top, and clost to the guage face. Or better still between the guage face and the glass, and if this is not possible drill holes or make a cutout at the top of the guage face itself.
It should not hurt with the same action at the lower part of the guage.
A lot guages has a slot at the top between the glass and guage face as it is this area that needs air circulation.
Goran
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