Years ago the Mexico Motel in Durango had large park like grounds with 10 or so campsites. It was right in town. Most of the land was sold so now it's a long and narrow property with just room for parking and the motel rooms. They would probably still permit RV parking, but to get in there would take skill and backing from a one way busy street.
We stayed there this last March, traveling by motorcycle. Just about every other hotel in town was booked, we felt fortunate to have a place to sleep. The rate was $22.50, people in the next room partied until 3am.
Like many Mexican cities Durango has grown exponentially since we started visiting Mexico in 1999.