Portugal is different
As you can read in in the Portugal-section of the (static) website, the rules for alternative building here are less strict in certain (agricultural) areas than they are in urban and coastal areas.
The reason for that is that many regions in the north and the centre are facing a decline in numbers of young people: most of them go to the big cities to find work.
Next to that the Portuguese system has one layer of authorities more than most other European countries, and the lowest level is the "freguesia" (the lower-mayor and a few other officials). They have a huge influence on this local level and often they have a more liberal view to the matter of alternative living-styles.
Many people live in a campervan or caravan on their land. Some build strawbale-houses, some build wooden houses and some use seacontainers as a basis for building.
Below a short video to give an impression of alternative building-styles: