Ok, I think I figured out a workaround to the transparent image problem.
I created another face 1/1000" in front of the surface of my ship that I wanted to apply it to. I projected the decal and painted the material onto THAT face, so that when you see through the transparent bits you're seeing the 'real' face 1/1000" behind it. As long as your surface isn't extremely curved, this should work without hours of building out a new surface. I also hid the edges of both surfaces. You'll also have to decide on the color or material of the surface, because changing it would in my mind require that either you go into the model and change the colors from the inside, or you would need to delete the face with the decal on it, change the color, then rebuild and reapply the face.
I've tested this in the Twilight Render plugin as well as Kerkythea, and so far so good...
Now I'm off to make weathered insignia and markings for my fighters! I'm going for the battle worn X-Wing look, and on old plastic models I'd simply use fine grain sandpaper to sand through and rough up the decals a bit. This is slightly more involved, but I think I finally found something that will work for me!

Hello all-

I've been working with Sketchup for a month or so now on a very sporadic basis. I've designed a starship bridge module and a fighter to go with it- I am an aspiring sci-fi writer and figured if I can provide a few images of my technology it might help my cause if I ever try to track down an agent or publisher. I'm stuck now on the details of my ships.
I want to place some images/decals/stickers on the fighter. I'd like to do some exhaust stains and carbon scoring plus some faded decals (for the bridge, I'd just like to do some keyboard/control panels that I've just stuck on as exploded images). Just as a quick-and-dirty, I made some carbon scoring png images using a black paintbrush with low opacity, plus a decal that I managed to make look suitably weathered. I even found tutorials on how to apply them to curved surfaces.
I'm stuck, however, on the transparency. I want the carbon scoring to sit on top of the hull color, and I want my decal to have faded through to the hull color in places. My decal is a long, swooping line, sort of reminiscent of the Nike swoosh (but not). The problem is, when I texture the decal onto the surface, I either end up with the white background painted on in addition to the decal, or if I import an image with a transparent background, it makes the entire panel transparent and I can see through to the other side of the ship.
What I need to do is apply the decals OVER the hull surface, leaving the original surface there. This will allow my decal to wear through, it won't cause holes in the hull where transparent parts of my background image are, and it allows me to change the hull color and material without having to start over.
Did I miss something easy? I've searched the forums and tutorials, but have only found a few references to this being a bug that will be fixed.
Can anyone help?

Thanks,
Ryan