I would not recommend dog diapers. Some dogs got trained with diapers, and they ended up urinating on the exact spot where you had diapers during the training period - meaning that without the diapers, they will do it right on the floor.

Crate train is the best method. Even if he has accident in the crate, clean it up right away with "Miracle" stain remover. Leave him in the crate at all time when you cannot monitor him. He will learn not to have accident in there because it is his dent. When you are ready to take him out for potty, immediately take him out of the house and ask him to go.

My dog had accident in the house when I just adopted him ( he was already house trained), I had crate trained him for 2 weeks straight, and he never had accidents ever since - nearly 4 months now.