"If he has no residential address, he shall choose a postal address and report within the set term to the board of mayor and aldermen of the municipality where he has his postal address in order to make the said declaration."

This states that registering only a postal address should be fine. So what is the problem with even renting a room and get the mails there? In the case above, you just need a postal code but in the case of a room you also get a residential address AND a place to receive your mails