If you can swing it get an enclosed right off the bat. A lot of it will have to do with how the ztrs front cater arms are set up. My Gravely are short and the Hustler SZs are long. Oddly the Hustlers stack better than the Gravely because they straddle the rear end of the mower in front. I now am running a 20' open car hauler and have two ztrs, one hydro walk behind, and a push mower comfortably. This also allows just enough room for a rear bagger on one of the ztrs. Keep other options in mind as well like bagger, thatch rake, front mount aerator,spreader, sprayer attachments if you have or consider getting any.
Here's a nice open one. I know it's too far away for you though.