I had the air bags on my F-150 that went inside the coils. Worked great. Even in -40f weather all winter they hold up. Once in a while they need a shot of air. But they are very durable from what I have seen. Even mud and dirt the gets trapped doesn't seem to wear through them.
One note, you have to maintain a certain pressure to aviod complete bottoming of the spring which can pinch the bag.
The ride on my Ford was firmer but it felt more solid. The rocking motion was almost taken care of. The front end sag was elminated. I wish I could put them on my Ram. If someone only made a coil & shock mount that put the shock outside the coil I could do it.