Retirement benefits

Direct deposit to a US bank checking account is the best way to go for me. Then withdraw from ATMs in Vietnam as needed.

Here is a relevant publication
https://www.ssa.gov/pubs/EN-05-10137.pdf

This pub was revised in April 2016. I'm sure I remember seeing Vietnam listed last year as a country where they would not mail your ssn check. I will assume another change due to recent US/VN romance over TPP and Paracels.

And this page shows Vietnam is listed in the section for Countries without international direct deposit.  Even though 3 people are, plus 126 getting checks. I wouldn't count on that.
https://www.ssa.gov/deposit/foreign.htm

Besides, it can be difficult to take your money out of Vietnam banks later.

Thank you so much-that makes sense! That's how I was planning to do it! As I have it now- I can draw anywhere in the world to fit my needs! Bravo!

Legal maintenance of a bank account in the US requires a physical residence.  If you do not continue ownership of a home you may need to rely on either parents, adult children or a trusted friend for the nominal address even if you bank entirely online.

My guess is that part of the US objection to the Vietnamese system is probably two-fold.  One, as Gobot said, they may not have agreements that let them dip into Vietnamese banks to recover payments made after your death.  Two, the Party is conflated with government, as the Party intends it to be, and most vital statistics seem to be kept at the very local Party level, often by hand.  The Party keeps track of people through the house book system and as a foreigner you may only be temporarily registered where you live.

Another solution is to have your check delivered for pickup at the US Embassy or consulate but that would be rather impractical for anyone not living in Hanoi or HCMC.