June 2003 Model Railroader. "Painting" with Decals.
What the author did was to "paint" a N scale caboose using decals he printed for the entire car. He painted the cab light grey so the decal colors would show well.
His settings include selecting a glossy paper, such a glossy photo paper so the printer would only place enough ink on the paper to prevent extremely long drying times. He also suggests increasing the contrast and reducing the brightness of the photo used to make the printer print good color (standard contrast settings would yield a faded version while standard brightness would make some colors to overpowering).
His N scale cab looks pretty good and it is one that has a lot of tagging on it which would be hard to do any other way.
I don't know if I would attempt to use a solid sheet decal to "paint" anything bigger than an N scale model. Even at the he had to cut the decal in 3 pieces for the sides.
but hey, it worked for him.