At least he has done the right thing and paid you up in full, I'd rather be waiting for the guy to pick it up than be trying to get payment out of him. As long as he keeps in contact and you come to a mutual agreement about storage fees if it is not picked up by a certain date I can't see any probs....

Tell him you need the space and will have to charge a storage fee if he hasn't picked it up by the agree'd date.