I'm not at all convinced your dog can make these higher level connections.
Dogs have a teeny attention span. If you CATCH your dog peeing in the bed is one thing - and if so, a loud NO! and bringing the dog outside immediately (to finish the pee there) is a good idea.
But if you do not catch your dog in the act, and 'punish' your dog after the fact, it can not associate the punishment with the deed. Therefore it cannot learn anything, and is unlikely to 'get it'.
15 seconds after the pee is too late. You need to catch the dog AS he pees....
At this point though....the residual urine smell in the bed might be enough to attract the dog to pee there. You'll need to clean that bed SUPER well so that the dog can't smell it. Perhaps others in the forum can suggest a great cleaner if they feel it might help.