You have it right but at the same time wrong.
What is needed is a “Secondary”. That is, conservatives under all their various guises including the Tea Party must hold a Secondary. That is, there must be some across the land preliminary conservative vote to select a candidate for the Republican Primary.
The primary will be very different if conservatives can coalesce on one candidate to oppose the presumed GOPe candidate.
A Tea Party Convention as a third party proposition is weakness and is certain to be defeated. Splitting the Republican vote will assure a Hillary disaster
The idea of a Tea Party Convention is not to establish a third party. The purpose is to confirm the choice of a presidential candidate within the GOP as voted for by Tea Party groups.