
I've never used a crate, but it sounds like everything you are doing is good for
crate-training (positive association with crate), but is doing nothing for seperation anxiety.
He needs to know thet you will be coming back, so being on his own is then no big deal, for this to work, you have to start of gradually. It sounds as if he is already fine with you leaving him in one room while you are in another, so you now need to focus on getting him used to you going out of the house. You could start by walking out of the front door (while pup can see you doing this), and returning right away. Graduly increase the time you are outside, making sure you return BEFORE he gets upset. Every time you leave him for long enough for him to get upset, it will only make him worse.
Hopefully somebody can give you some better advice on treating this, but it sounds like it has nothing to do with the crate atall, it's about him not feeling happy on his own in the house.
>It is not helped by talking to other dog owners when we're out and finding that their puppies are fine about being left for a couple of hours!
My dog, now 2yrs old can be left for several hours with no problems, but I wouldn't dream of leaving him as a 15 wk old puppy, for more than 30 mins
(just enough time to get the kids from school),
any longer than that and I would get a dog-sitter in (my dad/mum/sister :) ).