As you said, you don't know his background. I had a similar situation with Benson when I adopted him, and I later found out that he was crated a lot by the "show homes" that had him and the family home immediately before me. That family also kind of gave up on potty training and crated him a lot and used belly bands when he was loose. Benson also drinks when stressed, so that adds to the problem.
I made the mistakes of giving him too much freedom of area too soon, assuming he was more reliably trained, not taking him outside often enough, and not paying enough attention to when he was drinking. There are more things that could be adding to your problems too. I had a friend that adopted a former show dog, a large std poodle, that had equated walking through a doorway with the exit from kennel to outside run/potty area and would relieve himself almost every single time. This was inside the home and happened a lot.
Once I found out that Benson's former family failed him on many levels, I treated him much like a puppy in training and that is what I would suggest you try with your new dog. This entailed going out every single time Benson had been asleep and woke up, every time he'd been crated and was released, after each meal, and immediately upon waking in the a.m. before anything else. He was a little over 4 years old at the time, but he simply could NOT go more than a couple of hours without peeing, and he still can't. There was nothing medically or physically wrong with him at that time, but his bladder simply could not hold that much pee for 8 hours. Just could.not.do.it. We are pretty much still in that mode and it works for us.
When Benson developed the heart issues and was put on diuretics, I simply did not know how I was going to handle this additional peeing. Guess what though? He was hospitalized long enough that they put down pee pads for him and told me that he went to them right away! I was dumbfounded, and it was the one thing I hadn't tried! I now think that at some point in time he was trained to use them or was paper-trained. I still pretty much use the same routine with him as I wrote above, and even with the very high doses of diuretics he's on now, he is very reliable about peeing outside and most of the time does NOT need the pads. I do have them down in the kitchen for him, and the times he uses them are when I get interrupted with a phone call, when he gets stressed by being alone, and sometimes in the overnight hours. I also had to really pay attention to him to learn his signals, and to know when he drinks, and how long it is before he needs to pee after that. He does try to tell me that he needs to go outside to pee, but believe me, it is *very* subtle. That is something that you will have to learn about your new guy, and that is just something that takes time for you to get to know him.
Sorry for the long story, but I think you need to restrict your dog to a smaller area, do not allow him on the bed until you solve this, and take him outside a lot more often. More often excursions means more opportunities for you to reward him and a less full bladder if he does have an accident in the house.