I have a hard shell drum case, roadie grade, that is like 28" in diameter and 22" deep, it could hold the top assembly of a fairly large dobson.
Its a Hume & Berg Enduro case, just like this http://www.humesandberg.com/product_detail.php?product=730
really sturdy, with 3 handles and 3 straps holding the lid on. in Drum land, this is for a 24x18 bass drum, these sell for like $200+
I paid $75 for it sight unseen (my brother picked it up), but its way too big for my needs. The drummer my brother got it from used it on a national tour, so its scuffed on the outside...