I have to confess, I used to be vehemently opposed to third partyism and advocated for "reforming" the GOP from within. I used to make all the same stupid little unthinking arguments for "choosing the lesser of two evils" that we see people on this thread making. I woke up - they haven't.
My advice would be to just dismiss the "lesser of two evils" people and forge ahead without them. Likely, they'd just be dead weight in any serious movement to advance conservatism anywise. Keep building from the ground up, seeking to replace the GOP and it's establishment. When that happens, people like these on here will rally around once the GOP is visibly sliding, because following, rather than leading, is what these people do.
Keep building from the ground up
That's what has to be done in either case. After all, that's how the GOP began.