You have to make the lead a good thing.
Aye.
> Decided to get a choke chain to train him to walk on a lead.
>
> Only of any use if they are slack. It's the noise of them that does
> the job, not the tension.
Yep, no good if the dog is constantly pulling, as you often see. That isn't what you want. Keep the choke chain slack and when he does pull a sharp jerk to pull him back but straight away the chain is slack again. He'll soon get the message that pulling is not a Good Idea and that walking nicely with a slack chain is. You may feel you are constantly jerking the chain to begin with but dogs are not stupid and will learn.
He'll be rather disoriented - owner gone, all familiar surroundings
> gone, food has probably changed, all routine is shot. But you are
> being good to him and feeding him, so he's damned if he's going to
> let you go. Fair play really.
Yes, he's doing his very best to please and is showing he really wants to be with you. Grovelling springs to mind.
Does he have areas which are 'out of bounds'?
Good idea decide now any areas that are no-go for the dog and stick with them. With all the other stuff, the lead and overly pleased, don't be to strict on keeping him out. But make sure that he his never allowed to stay in a no-go area, shoo him out, firmly if required, I wouldn't shut a door on him at this stage but just repeatedly take him out of the no-go areas. When you do emerge, make a fuss of him, as a reward for waiting outside.
I'm afraid 1 week trials are convenient for potential owners,
A week also strikes me as too short for anything but the most placid and happy of animals to settle. I'd expect to see some improvement in a week but not a change to the well trained and obedient member of the family that one is aiming for.