O went through a phase of taking his nappy off too but he wasn't quite ready for potty training at the time..I think he just found out he could so did lol
He too used to go stand in the corner and do a poo.
But if Lewis is actually telling you when or after he's done it, it might be an idea to introduce a potty in the room. We had one laying around from when O was about 1yr old, but he hated sitting on it.
I would get one and pop it in the corner where he tends to go when he poops. Ask him if he'd like to sit on it, try with clothes on first and over time try when he's naky. I wouldn't go all panicy when he is doing a poo and rushing him on to the potty as that can cause anxiety when they want to poo to the point they end up holding it in for days lol
Let him have lots of naky time with his potty around. You might find that you and Sam have to sit on the potty so he gets the general idea lol (obviously not doing pee pees on it haha)
Just go with the flow and good luck