the solids you cite are all non-polar, which makes sense to keep moisture away. For them, I'd use a non-polar solvent, heavy enough to evaporate slowly at room temperature. Approximately a mobile lubrication oil, you have some choice among them.
Dissolution of solids or pastes in a thick solvent may take time, but you can heat. Powders dissolve more quickly. You might also add a light solvent which will evaporate first, possibly before applying the solution.