actually Vietnam has a pretty good relationship with the US nowadays. Lotta Viet emigrants in the US and they used to give a very favourable 1 year visa to US citizens.
I wasn’t sure that all crossings were possible for westerners? (Uk passport myself)
I have only crossed over into Laos and Myanmar personally and wasn’t sure of the situation in the south, knowing that Yala is a bit of a sensitive area 🤷♂️