Microscale's Micro-Set is a decal "setting" solution that softens decals and improves adhesion plus lets the decal conform to the model's surface.
To apply Micro Set: Use a soft flat artist's brush and apply Micro Set where you are going to apply the decal.
Then slide the decal off the backing paper using a small pointed tip synthetic bristle brush to carefully position the decal in its proper position.
Blot the decal carefully with a tissue or paper toweling, being careful not to disturb its position. Allow the decal to dry overnight.
1 oz plastic bottle, by Microscale.