Here’s my take on the Big Lost River Rest Area … there are 4 picnic tables with individual shelters to the east of the rest area. There is some reasonable grassy bits that are ok for pitching a tent. There’s no signs to say you can’t camp here, but equally no indication that camping is allowed. There’s a really good restroom building with a drinking fountain, and garbage bins. I think that parking up a RV for the night would be ok, but as for camping, you might feel the need to stealth camp.