Ron got just about 10% in 2008, his first Republican attempt at running for president and first ever caucus. This will be Rand's first attempt, so it's not too crazy to project him having similar results being the liberty candidate this cycle. As good as Ron was, it took him 2 runs at the presidency as a Republican, on top of a Libertarian run, to achieve his 20%+ results in Iowa in 2012.
I know we all want Rand to break everything open and shock the world here, and to some extent he definitely will when he outdoes all these ridiculous polls in the last few months, but I doubt he is going to get more than his father did.
People will say "well hey, what about the fact he has all those precinct chairs, he has way better ground game than his father ever did, and he's going to basically be living in Iowa right up until caucus night". And they are right. The problem is that Rand isn't as appealing to the same liberty movement that his father helped create and those were the people that showed up in droves to propel Ron as far as he was able to go. I think these two competing strengths and weaknesses going in here will balance this thing out to around 7-10%.