Incidentally, Penny mentions auditioning for it in the clip attached to this post from BehindKink.com. From her own words:

"I'm ashamed that I'm not ashamed."

http://news.behindkink.com/blog/default/2009/03/26/The-Pussy-Wagon-is-Back-for-more-PornStar-Confessions
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"I always find it funny when chicks say that, because I hate sex but I still have it. Afterwards, I hate myself, I feel awful, dirty and sometimes cry. But it's worth it, if only to feel a little human every now and then."