They are the basic firestone bags. They sit inside the coil, not attached to anything. The air plumbing runs up through the top of the sping. In theory, they should limit travel. I on the other hand have never noticed and if they do, its negligable. I was originally going to remove them becasue the tourflex springs do such a great job of keeping my rear up when towing our opus. We just sold the Opus and moved on to a larger TT with a more sunstatial tounge weight. I will be leaving them in to see if ill need them.
Your supposed to keep them at 5psi to limit any potential damage when not loaded. To be honest, when I'm not loaded I take out the valve stem cores and run them at zero. I have never had an issue like this and im confident they dont limit any articulation. I could see the plumbing failing before the actual bag is damaged on them. Also, they are really easy to install/replace, not too hard on the wallet and the benefits when towing validate the risk for me.