How about 12vdc trace heating wrapped around said instruments get it to switch on under 20°C.

Or mini 20mm fans fitted to the cases to circulate the air through?

Desiccant packs inside and sealing the gaps are another simple option.


Mark - No Longer driving
Archie the Old English Sheep Mog...........
2010 Roadster 3.0 V6 (S3) wink