You can wrap it in newspaper if you want, then ask for their flyers to put your item in.
They don't help to wrap.

Nah, should be fine one without a box. Keyboard sized boxes aren't easy to find as it's an odd shape (usually those boxes come in cubes one). If you don't want to buy, I suggest just wrapping a lot of newspaper, add in cardboard pieces if you have, then wrap everything with clingfilm before wrapping with paper again to make it water resistant

Follow what electronicfly says.
Important thing is to make sure water won't get in easily. Especially these days always rain.