evisa

In Oct/Nov 2018 I will travelling to Asia on an Holland America Cruise ship that departs from Shanghai and makes 4 stops in Vietnam (Halong Bay, Da Nang, Nha Trang and Phu My).
the evisa sites says that the final documents will need to be given at the arrival airport. As we will arrive by sea at four different ports and not airports, what should I do?

Thanks