RV parking at the Invitational is expensive but convenient. The OCCC does not have electric hookups so large generators have to be trucked in and wiring laid out. I imagine a support staff for the generators is also required. Also, the RV parking occupies prime parking space. The OCCC currently lists parking at $15 per day. Thus if your RV takes up four spots that is $60 per day just for the space.
There are numerous campgrounds in the Orlando area. The closest is probably Bill Frederick Park at Turkey Lake (close the info box on the road map and you will see it). It is a city of Orlando park and it used to be the site of an agility trial in October. The year we went we (and a few others) stayed at a KOA near Kissimmee and I shuttled the wife and dog back and forth.