I would not recommend coming to St. Louis if you're traveling in an RV. If you have to though and are looking to stay downtown this place isn't bad. Clean bathrooms, gated, reasonably safe (at least we didn't have a problem while parked in the park itself).
That said, I would NOT recommend parking your RV anywhere else in the city. The city is riddled with crime and car/RV break-ins. It's on an epidemic scale and burglars specifically target cars and RVs with out of state plates.
We parked on a city street outside Pappy's Smokehouse on Olive St. and within 30 minutes someone had broken the lock on our front passenger door and stolen $7000 worth of valuables inside our camper. We are in a class C - id say a class A would be safer with only one coach door with a deadbolt. Our class C has too van doors in the front and they got in very easily. Be very aware of the surrounding areas - don't leave your RV parked unattended on ANY public street. Just assume you will be robbed if you do. Not worth losing all of your belongings. The police weren't optimistic that we would get our stuff back - they said this kind of thing happens multiple times a day and they don't have the resources or time to deal with each case. Park your RV or camper in a secure, gates area and take cabs/ubers to wherever you want to go in the city.
Honestly though, my advice is to stay away from St. Louis/most of Missouri altogether because it's just not safe for anyone.
