We normally call ahead and see if they have RV parking. Many places might not, but they can usually suggest a place and give you a plan.
My favorite was at Zion to avoid the escort through the tunnel (entering from the East) they said I might be able to park in the turnaround just past the "toll booth" and drop the 5er. They had a warning motorized sign about the tunnel. Perfect, a 10 foot hole behind the sign, so I did not even use up any of the turnaround. Ricky the Ranger liked that bit of thinking.