This is not uncommon.
The more recent Morgan instruments have breather holes in the back of the instrument case - make sure these haven't become blocked.
For older dials that do not have these holes, some owners have drilled their own small holes to allow the condensation to escape. It goes without saying that if you drill the case that (A) be careful where you drill as you do not want to damage the internals and (B) ensure you do not drill a hole that is too large and therefore allows contaminants into the dial (a 3mm bit would be ideal).
Driving with the instruments lights on, all the time, can also help.
