Most people will rent paddocks, but ideally, a barn has a farm off-site and can rotate showing horses on and off the grounds. I would never keep a horse in the temporary stabling there for all 12 weeks...
Back when I was grooming we never had paddocks ( but there were a lot back then). We would handwalk/graze a lot and trail ride when possible. Horses always did fine. Once in a while we would be told to "borrow" a paddock, I hated doing that, most people would put padlocks on their paddocks for that reason!
I'm with Tha Ridge. I'd never keep horses there for all 12 weeks. The year before last there were "paddocks" available - terrifying really. Wayyyyyy back in the corner of Littlewood and in the middle of where all the trucks and everything drove through. Not worth it. I don't think those are available anymore. There are also some paddocks in the corner where there are some private rings behind the woods by some of the tent stabling, but I've only seen some stock horse types in there that look like they live there year-round, so I don't think those are for rent either. The lunging is kind of a joke anyhow - the designated lunging ring that is available all day is small and the footing gets deep quick. If you're up early you can get into some of the rings, but I wouldn't want to lunge anymore than needed to anyway.
I suppose if you HAD to keep your horse there for 12 weeks with no paddock access, I would do a stall and a half for sure (we do it anyway just because the temp stalls are so small) and do A LOT of handwalking and finding what grazing you can. Having a horse with no turnout available that is used to having it is just asking for behavioral and possibly soundness issues, in my opinion.