So can i park here over night and sleep in my van? Or is that a no no?

I don't know the policy, but other people do it at the very end of the road.

Signage at the rest stop says no camping, but using the rest stop over night, if one is tired seems in the spirit of things. I was not hassled recently (late Oct 2020) when pulling in overnight, but maybe different in the summer. Restroom is clean and warm. Taxidermy display is interesting. There is a dump station. Apparently in WY semi truck and RV parking overnight at designated parking pull offs is permitted. In eastern OR overnight at rest stops is permitted.

I believe that it is no overnight parking