I grabbed a baby gate, and with the help of my daughter, we wrestled Rufus into the doghouse, then I set the baby gate in front of the opening.
I had to sit on top of the doghouse, in the pouring rain, so the baby gate would stay in place. My daughter ran back inside our house to watch out of the window and laugh!
I sat in that downpour, on top of his shelter, holding the gate in place, for close to 20 minutes!
During that time, I never spoke a word to Rufus. Obviously, I was muttering to myself about having to do this, but he didn't know that!
I waited for him to first get quiet and stop trying to paw at the gate. Then I waited for him to sit down.
Eventually he did lie down. The whole time I did this, I did not speak to him, I just totally ignored him.
After he finally settled down and had been lying still for about 5 minutes, I moved the baby gate, and came back into the house.
He, of course, immediately ran out of the doghouse. As I watched from the window, within a few minutes, he walked back into his shelter, on his own, and laid down.
That was the end of that. He came to love it like a den, and didn't appreciate it if any of the other dogs tried to use it.
Several years later, I had this happen with another one of my male Golden Retrievers.
This dog also would not go in his dog house, except this time, I didn't wait until it was pouring down the rain to correct it! I did the exact same scenario, in a very light drizzle, and the problem was fixed!
Sometimes dogs just have to be shown that there is no reason to be afraid, and the best way to accomplish that, is by simply, but silently, forcing the issue.