In scripture we never read about people preaching the Trinity or insisting that people believe it in order to have true faith in God.
Over the centuries many Christians have diverged and insisted that people believe in the Trinity as the foundation of true faith in God. While this belief indeed is the Roman Catholic Faith, Christians should never make this doctrine a requirement as it only proves to alienate people from the way.
In scripture we are told that stumbling blocks are inevitable, but woe to the them that lay them. Think about it, if you insist on this doctrine and it keeps a person from receiving the son of God, then you have contributed to blocking the way of salvation to that person.
We should be wise and stick to teaching what is written. God sent his son into the world to save men. He died for our sins, rose from the dead, and is seated at the right-hand of God and interceding for us. This is written.
Keep it simple. Simplicity in Christ. He is the son of the living God, the messiah, and the one whom God made Lord. There is no point in insisting on things that are not written, especially if they become the deal breaker from them receiving the son of God.