In the UK we have many 'fly tippers', so I would find an old leather sofa and cut a lump out of that, seat covers are only stapled to the plastic base these days, start at the front and stretch the material. Use the original as a pattern if you can, if you need a fully waterproof black cover the material should be easily available on the web.
That dog needs feeding more.
Regards and welcome to the site
Dave