Future over pastel chalk

I've had good luck using both gloss (Future, Floquils Crystal Clear etc) & dull (Dull Coat, DDV etc) clear coatings. And yes clear coating reduces the weathering effects of pastel chalks. To overcome that you have to over emphasize the weathering. When you reach the point that you think the weathering is where you want it, continue to apply the pastels. When you reach the point that you feel you've applied too much pastels, stop and apply your clear coating. The reducing effect of the clear coating will usually bring the weathering back to where you want it. You need to pratice on an old model that you don't care about.

I usually follow the following sequence:
A. Apply a coat of Future followed (after the proper amount of time has passed) by the application of the decals.
B. After the decals have thoroughly dried, over coat with a dull finish and then apply the pastels (they don't cling very well on a gloss surface)
C. After the weathering is applied I apply a coat of the finish I want (either dull or gloss)

When applying the clear coats, put on the minimum amount necessary to achieve the effect you want. It'll take a little practice to recognize when to continue or to stop in order to get the effect you want, but it's worth it.

Hope this helps a little

I've done it, but only once or twice. You have to spray at very low pressure and from a distance or it blows off. Also, if you leave the Future glossy you lose most of the effect of the chalk. It tends to blend in with the rest of the finish and loses all its flat appearance. I use Future mixed with Tamiya X-21 Flat Base and that works pretty well.