If he had been even the slightest bit reasonable I would have had no problems at all. "I'm trying to sell it, it should be gone in a weeks or so" would have been met with a "no worries".
An "I'm parking it here because I know it annoys you, and there is nothing you can do about it", which is what I got, makes me think that depriving him of fifteen large is reasonable rent. After all, he's had an entire year rent free. Hope he needs the money.