Best bet for good information is to call HQ. I would guess that on site registration might be limited by space available. My understanding with 30A electricity is that is someone cancelled out on such service, you might be able to pick up the slot.
I know folks in the past have parked at nearby RV parks in order to get full services and just hit the Rally for meetings and events and people.
It appears that WBCCI has had some problems with non registrants so they are being a bit more picky on registrant identification at events this year.
I know they are also picky about parking schedules. We will hit the bullpen Sunday because we aren't set for parking until Monday. So I don't know what would happen if somebody just showed up. If prior experience is a guide, I'd hate to think of the outcome. Some folks just have no sense of humor.
Bill, I'll see if I can catch up with you. One of our members has a power wagon. He traded two rifles for a 72 Safari and ended up so airstream infected he polished his trailer, moved his base to the wife's old family territory, and went full timin' - hope we see him again.