I'm looking at some self-drive options for barge rental in the south of France. Has anyone booked with Camargue Plaisance? Any particular boat recommendations?

I have not used that particular company, so I can't give you a recommendation. There are lots of others, though, so you can shop around. Here is a link that lists a bunch:
http://www.canals.com/french.htm
Just scroll down the list for those that say, "Canal du Midi.

What sort of boat you choose depends too much on how many are in your party, cost, and a host of other variables, for us to give you any advice. Give more details and perhaps we could help you narrow things down.

I've rented self-drive barges on a few occasions. A key piece of information needed is the number of people in your touring party. Let's know that, and we can proceed.

The other important issue is how "outside" the driver can be. Some barges require the driver to be isolated from the others and remain "inside".

We used Locaboat and went from Agen along the Garonne Canal to the Baise River.
It was my husband and I and 2 adult daughters. We had a 3 bedroom boat with 2 bathrooms. It gave us plenty of room for our luggage as we had all been travelling for 4 weeks beforehand. We could have had a smaller boat but we would have been too cramped.

I forgot to say that the boat could be steered from inside or outside. The weather was good and we were usually outside, sitting watching the world pass slowly by.

You will always need more berths than you think. We went on an 8 berther with 5 people and it was just about right. Also chose which side of the Beziers locks you want to do. The time taken to climb that mountain may be frustrating

And rent bikes as well.
We used Crown Blue and were very pleased with them.