A friend who served with the Army in Vietnam, returned before Xmas and toured and said he had no trouble with gay company.
He used gayromeo ,set his target under 24 and posted his info in as visitor, 6 weeks before leaving.

He said he had millions of contacts which suggests he got a lot of replies

He broke down his replies to

Hanoi. Ho Chi Minh and Da Nang. He included touring and got some interesting replies.

He missed out on boys in Hue, Dong Nai and Haiphong because of the time they were available, and his companion. There were a few others.

I recommend putting yourself in as a visitor and tell them where you will be, what you are looking for and an idea of price.
If you are touring north like him, place where you plan to be and the dates.

There was a problem with dates, which he said he had to add a day to his trip each end to get right.

Hope this is of help