I've used strips of red decals to detail the landing gear doors of my USN aircraft with success. I use a pair of dividers to measure the length of strip needed, cut the decal, and with a new no. 11 X-Acto blade and a steel straight edge, trim it to the correct width. Then with a 5-0 brush I apply a bead of Future on the edge of the gear door. Once the decal has been moistened and is ready to slide off the backing, I slip it onto the edge of the door usually with the tip of a moistened 5-0 brush or a needle chucked into a X-Acto knife handle. To strengthen the decal and bond it to the gear door, I apply another bead of Future once it has set up; usually an hour or so. I usually have to trim up the decal, both length and width, with a new X-Acto blade once the overlay of Future is dry.
The process is tedious and necessitates the use of a magnifying lamp/lens, but the end result is worth it. Hope this helps.
Dick McC