I have only done one aircraft in Alcad, and did not future before applying my decals. I had no issues with the majority of my decals- National markings etc. went on just fine. However I did have some minor silvering with some of the tiny stencil decals. The next time I do a plane in Alcad I think I am going to use future to set any stencils.
By coincidence I am working on a P38-J also. Have not decided if I am going NMF or if I am going to do a gray\olive drab bird.
The art of war is simple enough. Find out where your enemy is. Get at him as soon as you can. Strike him as hard as you can, and keep moving.-Ulysses S. Grant