Sudden changes in temperature and humidity are not good for any harp – it is the shrinking or swelling of wood that has the major effect on breaking strings. That said, nylon is more elastic than gut so you may have less of a problem but you will still be tuning frequently. Obviously the higher the tension the more likely tuning and breakage issues will be, no matter where you are.
If you (that’s a general “you” folks) want a small harp to regularly play in challenging conditions such as the beach, camping, etc. choose a nylon strung with high density ply laminate sound board (or a carbon fiber body if you can afford it). Go for practical over pretty.
Biagio