You could do a search at www.walthers.com until your catalogue comes. Right now I think Model Power is the only RTR or kit HO transfer caboose out there, but I think someone makes a kit to convert a flat car to a transfer caboose.
Of course a transfer caboose could be just about anything, from a shack on a flat car to an old wood caboose (often without it's cupola).
Go to the model railroad magazine index on this site and search for "Caboose plans" and you will get a number of them.
Dave H.
Dave H. Painted side goes up. My website : wnbranch.com