I lived in New Orleans for about 15 months, which biases my answer a bit. We stayed at Ponchartrain Landing RV Resort.
www.pontchartrainlanding.com
It was the only RV park that allowed long term stays that wasn't downright dangerous. I never went to the KOA, since it only allows stays of 2 weeks or so and is on the far west side of town, but it is probably a fine alternative.
Ponchartrain Landing is very close to downtown and the WWII museum. They have a shuttle that takes you to the French Qtr 3 times a day I believe, and you can probably get public transportation the rest of the way or taxi/uber.
It is a fairly large campground with a restaurant, bar and small store on site. It's usually quiet there and is close to grocery stores, etc. The staff is very friendly and helpful. There is a marina since it is right on the intercoastal waterway which leads to Lake Ponchartrain, about a mile away. There is a security fence that has a passworded gate that closes at night. They have a security patrol as well.
It is on a road which is on Port Authority grounds and upon seeing it for the first time it can be a bit shocking. The first warehouse you see as you leave the main road is dilapidated and unrepaired since Katrina, but it is the only one on the road that is like that.
Most roads in NOLA are full of potholes and this isn't one of the best, but they try to keep it repaired.
I considered camping across the lake at some of the places in Mandeville, but to get back and forth to the city you need to traverse the Causeway. It is the longest over-water bridge in the world at almost 24 miles. Look it up. The Causeway also has a very high rate of accidents along its length. I do not believe that RVs and trucks are allowed on it.
I found Ponchartrain Landing a very nice place to stay ... the only place to stay in New Orleans if you ask me.