Hi Sean,
They can be funny devils to work with but you can get superb results.
The problem that you have is that you used ordinary thinner, they need cellulose to succesfully thin them down. I always stir the tinlets well and then transfer a quantity onto a plastic food lid. Then using the cellulose thin the paint until it is about the consistancy of milk.
As you paint the surface, it is important that you watch and add a little more thinner to keep it flowing as it will thicken quite rapidly due to evaporation. If you dont do this you will see that it is not easy to apply as it tends to cease flowing.
My method is to avoid going over the same patch on the componant, build the paint up in thin layers and once happy with the result allow it to dry fully. Buff the surface withy a cotton bud and reapply the paint in another layer if you feel that it is not as thick a covering as you like.
With practice it gives superb results. You should also clean your brushes with cellulose thinner. I do believe that this is mentioned on the tin. If you thin it really well it will also airbrush really well.
John