score:3
We crossed the border yesterday and no proof of onward travel is required.
On the medical form in Vietnam, they ask where you are planning to leave the country and on what date, and also where you will stay. I have listed that it will be 'by bus' and put the same dates of entry/exit as on my visa. I didn't list where I will leave the country, nor an address where I will stay and all five of us went through a hitch.