I agree with your analysis. As difficult as it may be, it would be far, far more effective to change the Republican Party from within (while preserving a check on Democrat/Socialist/Leftist ideology) than to attempt to establish a viable third party that would likely take decades to achieve an electoral majority.
I do believe that this is the wisest course of action for the patriotic right, and for the security of the nation.
It will be far more efficient, and will take much less effort to vote out the non-performing RINOs in the Republican party, than to build an entirely new party.