I use Weber rib racks in my Smokette cause that's what I already had when I bought the Cookshack. They work just fine. No problem with slots being too narrow.
I find that the small end of the slab of ribs tends to cook faster than the rest so I usually lop off a few bones from the small end and chuck them in a zip bag in the freezer for future use. When I get enough for a meal I'll cook up a batch of small ends. Removing those bones from the slab makes it just the right size to fit in the 08. They lap over onto the sides a little but it doesn't seem to hurt anything. After a little while they will have shrunk enough that they'll be will clear of the sides. Works for me anyway.