Ever hear about Pykecrete, and the HMS Habbakkuk? This was a proposed aircraft carrier made of a material that was a combination of saw dust and ice. The ships could have been up to 4000 feet long, and 600 feet wide. The stuff was so tough they'd pretty much have been impervious to bombs or torpedoes.
http://www.royalnavalmuseum.org/info_sheets_Habbakkuk.htmAs to the DD tanks, I also agree they weren't so bad. One theory about the loss of the tanks at Omaha is that they not only launched too far out, but because of where they were launched, and the navigation point they were supposed to head toward, they were subjected to a strong crossing sea and that is what swamped them. If they had headed toward the waves, like the tanks at the other beaches did, they would have been fine.