We are planning a road trip in late July and would be stopping over in the area 9pm Saturday evening. It doesn’t look as though reservations are available at this campground - would we likely be able to pull in and sleep in our van, or out of luck?

If you're in a van there should be ample spaces. If you're flexible, I'd recommend pulling in on Sunday instead of Saturday.

Should be okay, there is no reservation for that camping area. It is 1st come 1st serve type of thing. If you are heading out to the wisdom area there is also a free American legion park there as well.