Caveat, as far as I know, LE has not asked for info about whether anyone saw the car before Wed, but one of the news articles said they know the car was there on Tues because it was seen on a deputie's dashcam video. Not sure what is known about the car's whereabouts Sun-Mon.
As far as I know, they never block access to that road because the road is used by campers & RVs to access the campground, so yes, the car could have been parked there most anytime from Sun-Tues.
I was at the park the Wed they found the car. Deputies had roped off the parking area, her car had the trunk & all doors open & there was a crime scene van there. As far as how much processing they did, I don't know, but since there was a crime scene van it would suggest they did gathered some " evidence".
I do know one of the articles I read said police searched the property around her home with a search dog, but as far as searching the house inside, I don' t know.
I do agree, if LE feels confident she is not in the park, doesn't make sense to tie up resources to do another search. However, since I, and a lot of others, frequently walk in the area where GF's car was found, would feel more secure if we knew abduction could be ruled out.