It sounds like there is water vapor within the gauge that then condenses on the glass interior under certain conditions.
Can the running lamps be left on overnight to dry the interior? If not, then can a jury rig be implemented that only powers the gauge lamps, for an overnight or longer?
My experience is that daytime elimination of interior condensation using lamp heat is impossible. My experience is that a towel draped over the gauges w/ those lamps on helps to eliminate that interior water / water vapor.