Of all the people that will be on the ballot, Pence is the only one even mildly Conservative. Johnson/Weld, Donny, Hitlary/Eyebrows and Stein are all big govt' Leftists. Castle is just plain fruitloops.
If you listen to the libertarians tell about Castle, that is the story you will get.
For instance, they call him a "troofer" (He wants the truth, the other 28 pages of the 9/11 commission report released, the ones which deal with Saudi Connections, where all the terrorists came from) He isn't one of those Bush did it, fired a missile, etc. types.
If you listen to Castle say what Castle says, and not a derivative account, it is a different story.
(Of course, the Libertarians are pushing to be THE third party, and they have the best name recognition, so they wouldn't say anything bad about other smaller parties, would they?)