I'm so sorry you are having to deal with this and the dog is being forced to live like this. I really don't have anything that I think could make your DH change his mind. It sounds like he has his head buried in the sand and I don't know what there is that you haven't tried already that could change that.
I do want to say, as a vet tech, that I agree 100% with whoever you talked to that told you this dog is suffering. Dogs are not humans, they don't have "memories" (they can associate things, but that's different than being able to go "remember when..."), they don't have a concept of the future, all they have is the moment. This dog is having bad moment after bad moment and, at 16 yrs old, there are no good moments in the future. I can deal with sick/injured dogs and cats hating me/attacking me and still have sympathy for the animal because I know they are just living in the moment. They don't know that what I am doing will make them feel better, but I do. In the case of your bassett though, there is no feeling better in his future. Their is just pain and more pain until he dies. So again, I'm so incredibly sorry that you and the dog are having to go through this, but if it's any consolation I think you are 100% correct in wanting to euthanize this dog.
I'll leave you with my favorite quote in regards to euthanasia. "The greatest gift we give an animal is to take away their pain and make it our own."