As a thought, because you mentioned airbags...
I was having a lot of bob and sway with my camper, which is smaller and surely much lighter than yours. I picked up a set of Timbren springs. They have drastically reduced the mushy, swaying feel, and are completely maintenance free. They also don't affect the ride one iota when the truck isn't loaded. And I don't ever have to inflate or deflate them as a part of my loading or unloading ritual. I'm not saying they're better (I've personally never used airbags) but they are a definite option to consider. I picked mine up on craigslist for $100 and had them installed in a leisurely 1 hour.