Here is one of the centerpieces for my Mariners Blight Army, a Contemptor Dreadnought modified to look like an oversized deep diver. I drew inspiration not only from actual 1800's diver outfits, but also from Big Daddy.
I took the Forge World Dread and added some subtle Chaos trim with Greenstuff and Styrene rivets. I used a Chaos vehicle spotlight (Which fit perfectly) as the diver helmet. And then I sculpted the tentacles from greenstuff as seen in this post.