I sometimes find that the temperature reading on the Alde panel is a little bit all over the place,it seems to over read or under read on occasions.
I was considering buying the Alde remote temperature sender until Pebble ( Paul ) on Caravan Talk came up with this little gem which is certainly worth a try,if it doesn't work well nothing is lost.
First of all it appears that the temperature probe on the Alde panel is situated inside the facia cover and not exposed to the external air,arrowed in photo below,so it is hardly surprising that it is not too clever at judging the external temperature.
The idea therefore is to drill a small hole in the edge of the facia cover at the point where the probe is situated to allow it access to the air.
Refit the cover and bingo the temperature readings should be more in line with the exterior.
Incidentally the facia cover is easy to flip off with a fingernail.
I will try it out on our next excursion and report back,as said previously if it doesn't work nothing lost.