Trump's base is not providing the RNC funding as it is - so that is no big threat. Most of Trump's base are the ones that are pissed off with the RNC and stopped giving to them a long time ago.
...start new party if the GOPe backstabbers refuse to give up control of RNC.
I think they would probably be okay with that in the long run. It wouldn't have much more long-term impact than the Reform party. You can't have a national party based just on a presidential candidate. The reason the Reform Party, Libertarian party, Constitution Party, Bull Moose party etc. never took off is because for a party to have a chance at the national level, you also have to have congressmen, senators, state legislators, etc. A Trump party might be able to elect Hillary, but they would not be a factor in 4 years. Then the Trumpkins would either go back to the GOP or Dem party from whence they came, or would go back to being uninvolved as many of them were before.
But some of them have this fanciful narrative in their heads that Trump can - somehow - get everyone to submit to him. The truth is that he has very little leverage, and the more he attacks the party itself, the less leverage he has.