Most RP supporters are just people that think the federal gov should just get out of everyones way. You say that RP supporters are mostly nutjobs but that isnt the case. Sure, the conspiracy types def. tend to lean towards him, but they are the minority in my experience. Of course, the media tends to highlight them, and deny coverage to everyone else. Similar to how they go out of their way to make him look bad every chance they get.
There is a reason this happens. His ideas threaten both the federal government and the large corporations who are in cahoots with them. He's not a nutjob, but an America with constitutional values isn't going to go over well with all the people with crap-loads of money and power that would be vulnerable in such a case.
The ideas of limited government (both civil and economically speaking) isn't outlandish, it's common sense. The idea of a military that is focused on defense and not offense isn't isolationism, nor is opening up trade to any and all countries.
