I am assembling a Lanier SeaBird that almost the entire thing is plastic. It came with a very small bottle of what they have labeled aero-cement. When one applies it to a surface it seems to make the surface soft so that when you put the other piece on it, it kinda welds the two together. Problem is: if you leave the cap off the liquid evaporates very quickly and now I don't have enough left to finish the project. Any ideas what this is and where I might buy some more. It says it contains Ketones, what ever that is.

Could it be as simple as PVC Cement for pipes?

PVC cement will destroy the plastic on the plane. What you need it cement designed for this type of plastic. The best cement is called IPS Weld-on #4. You can buy small bottles of it at any hobby shop that sells plastic models. If you can't find it at a hobby shop you can go to a glass shop, the type that replace windows. They use it for working with Plexi-glass. You should be able to buy a quart of it. But as you already know, make you leave the lid on it. Transfer a little bit of it in to a smaller bottle to use while working on the plane.

Ken