Let me put this in perspective. Rush is fairly pro Cruz, but he's given the Trump campaign about 360 million dollars worth of free positive publicity since June. He mentions Cruz maybe a 50th of that much. He hasn't endorsed officially, but his entire program has been a Trump Show since June.
Second, four years ago he totally skewered Newt when Newt went LEFT of Mitt with the Bain Capital ads. And Newt deserved it. This cycle, Rush is floundering around avoiding doing the same to Trump. Rush has abandoned what he stood for over 28 years for his own fan boy infatuation.
Insofar as Trump goes, I think he's made it quite clear in the past two weeks (although he doesn't officially endorse), that he would prefer Cruz.
As to the free publicity for Trump, I don't think that was so much true, certainly not on purpose from Rush. It was the strength of Trump's ability to form the narrative, to force himself to be in all of the news that made that possible.
One thing is true about Trump: He knows how to manipulate the media, he knows how to form a narrative. It's his greatest strength.