Most Caucuses are by secret ballot. We run ours that way.Republicans caucus by secret ballot. It isn't like the Democratic caucus. Actually, I'm not sure why they even call it a caucus, if it's by secret ballot.
However, that doesn't change that a caucus only brings the most activist of voters. Of the 2 Million people registered to vote in Iowa, there will be a bit over 200K of them that caucus, and that only because caucuses are a bit more important there. In contrast of a bit more voters registered in CO there will be about 40% to show up for the Primary about 20% in an off year.
Therefore flooding the caucuses with the Religious suddenly makes them overrepresented at caucuses. Hence the reason I tell people that if they don't want the party run by the Evangelicals they need to get to the caucuses here too. Otherwise the vast majority of delegates are from that group too and they get to select the Primary candidates.