Any cover made for a Weber kettle will fit quite well on the BS Oven, with the side shelves removed. I put them inside the oven, on top of some cardboard. I prefer to store without side shelves on, saves a lot of space.
I have the factory cover, and do not think it is worth the price. While it is made well, the material fades in the sun like no other cover I've had, and I have LOTS of covers.
Weber kettle covers are made by Weber in multiple quality levels, as well as aftermarket manufacturers in all price ranges. I have some poly covers that I bought at Kmart end of season sale that were <$3.
You should have to have the BS Griddle
and the BS Oven to be part of the "Blackstone Posse", because the BS Griddle is equally as awesome as the BS Oven.
Congratulations to all the new BS owners, and Bravo to all Brethren who helped facilitate the discount purchases, well done!
Insane amount of info about the BS Oven on Pizzamaking.com, where you will find many Brethren already posting.
http://www.pizzamaking.com/forum/index.php?topic=25127.0