He obviously took advantage of your generosity and personally I think your doing the righ thing by giving him a hard deadline to meet before your take even more drastic measure's. The problem with that is that he obviously doesnt see any value in anything he left there or he would've come back or, like you said, made time to come back and deal with it so what good is it going to do by selling it? It will get back your money (hopefully) but it doesnt seem like your going to get any sort of "payback" at him for selling his junk. You'll probably be helping him out. So it seems, selling his junk may just solve both of your problem's. You get your money, and hopefully a bit more. And he gets to just forget about anything he left there.
So, the obvious question is, did he leave ANYTHING of value there? And if so, do you think you can make any money selling it?