You really don't know how lucky you are!
Take him out in the rain with a big golf umbrella - I do. I take Lucy out late at night too. I use a big bright lantern. When it snows, I take a shovel & make a path for Lucy to walk in & she wears a nice down coat.
You may confuse him if try to break him of going only outside.
He really shouldn't be alone long enough to have to pee inside.
I say keep him going out of the house if possible. Good luck.