These commonly seen snap handle drain plugs are similar to the ones you see in Wal-Mart, but these are Stainless Steel, not zinc plated steel. They will not rust. Any reasonably smooth 1" hole in a transom or other location will work. You can install a section of tubing or simply line the hole with epoxy. Plug tightens by folding the handle flush as in drawing in Particulars.
Below is a picture of a regular plated steel snap handle drain plug after only a short time in fresh water. Imagine what it would look like if it had been in Salt water. Our solid stainless steel drain plugs will not rust.