Microscale's Micro-Sol is a decal "setting" solution for the most difficult irregular surfaces to be found on models.
It allows the decal to drape down onto the surface of the model, conforming perfectly to surface irregularities without distortion. You should coat Micro Sol on for only a few seconds and then leave it alone. It does the work. Do not touch until the decal has dried, as the decal is very soft at this stage and could be easily damaged.
See my blog page on using Micro Set.
For the best results, first apply Micro Sol to prepare the surface and enhance the adhesive.
Make sure the surface is free of particles that could get under the decal's film and cause a blemish.
Then, when everything is dry enough that the decal will not move easily, apply Micro Sol with a small flat brush.
Apply with as few strokes as possible so a not to disturb the decal.
Then allow the decal to dry without disturbing it. One application is enough in most cases but, if necessary, a second application of Micro Sol can be helpful.
1 oz plastic bottle, by Microscale.