Hi eyeball, as the other guys said you really need a gloss surface if you are applying waterslide decals. The decal kit you saw probably contains two types of decal setting agents, Sol and Set. One you apply to the area where the decal is to be placed. The decal is then slid into place.When you are happy with the positioning of the decal gently press it down to remove air bubbles. I use a soft sponge for this. Try to avoid using a wiping motion so as not to move the decal. allow it to sit for a few minutes, then apply the second solution. Do not touch the decal except lightly with the brush whilst applying it.
The two solutions do the following. The first softens slightly the underside of the decal and improves the adhesion. The second softens the upper surface. By using them it draws the decal down onto the gloss surface and into any panel lines or slightly raised panels etc.
If you do use them and the decal starts to wrinkle DON'T PANIC. This is normal. The decals should be left untouched. I usually leave them overnight. Sometimes if they are applied to really uneven surfaces another application of the second solution is necessary. Eventually the wrinkles disappear and they really do look like they have been painted on once they have been sprayed or brushed with another coat of varnish, gloss or matt.
Hope this helps
Martin