I was hoping to get a response before trying to give you a reply but I don't want you to go to long without one. I can think of a few possibilities. One would be that he has no clear signal to use in the caravan like he had in your home to let you know he needed to go out to eliminate. so I recommend a clear signal be employed. Put a bell or other noise maker on the door low enough for the dog to reach. Each time you take the dog out, ring the bell. The dog will associate ringing the bell with going out and one day ring the bell to signal to you that he needs to go out.
You state that you have already changed feeding times, so I want to suggest that you keep a log of when you feed and when you water him. Then track when he defecates and uinates. A pattern usually emerges for each dog in just a few days. You can then adjust the feeding and watering schedule appropriately so he is eliminated when you are able to have him outside.
Given the age of the other dog, it is also possible that he may have picked up a parasite from the pup making it harder for him to control his bowels. Parasites or a protozoan infection will make it harder to control their bowels. You can take a fecal sample into your vet for testing to rule this cause out.
Your dog might also be experiencing fecal incontinence. Fecal incontinence can occur due to some medical issues such as perianal fistulas, trauma to the anal sphincter such as can occur with anal gland expression and disc issues With disc issues, you might notice that he doesn't jump as well or avoids the stairs when possible. This might be something to also discuss with your vet. If a disc issue is just starting, he may just find it hard to control the bowels. Often dogs with this problem will defecate without even seeming to know. In this case bulking up the diet with fiber such as canned pumpkin (not pie filling) or metamucil might help stop the incontinence.
If a medical cause is ruled out, then re house training him would be the best way to take care of the problem. You could use the same method you did when he was a pup or use an alternative method. Since it happens over night, I'd probably use crate training. You can read about this here:
I hope this information is helpful to you and you are satisfied with my response. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have .