I agree with some of these theories Jonnie. Corrie could've well gone looking for a quiet area to pee and disturbed a drug deal. You make a good point of the person exiting the area not wanting to hang around if that's the case. I know there was no evidence of a altercation at the Horseshoe but unless he was bleeding outside the car there wouldn't be any. I would imagine there was more than one person there, and the more people the easier it would be to bundle him into a car. Before or after possibly harming him that is. Looking at the photos it seems the far corner is well hidden from the main path, especially with vehicles parked there and would be a perfect spot for any dodgy activities.
The only thing I don't go with is your suggestion of him possibly going in the bin, one for the reason you stated (difficulty lifting him) and the other being that it has been ruled out in the investigation, weight, forensics etc. It just seems far more likely his phone was thrown away by someone else. Also, if his phone fell out his pockets then what about his wallet and keys? He can't be traced by those so they're not as important to discard. The more we find out about the more convinced I am this is what has happened to him. Sickening thought though.