Testor Dulcote

It should be be safe enough.  Make certain though that you let the acrylics underneath cure for several hours and preferably overnight.  When spraying Dullcoat, be mindful that you apply light coats.  What you DO NOT want to have happen is for it to puddle up at all because that is the type of situation that will lead to the lacquer solvents eating into the underlying paint.  I used to use Dullcoat over enamel with miminal problems.

On the other hand, I think that Dullcoat is not the best flatcoat out there.  I've always heard very good things said about Ployscale's acrylic flat coat.  If your local deal doesn't carry Polyscale, you can make your own flat by mixing Future and Tamiya X-21 Flat Base at a ratio of 4 parts Future to 1 part Flat Base.  I use Future/Flat Base now and prefer it to Dullcoat.  I find that I get a better finish and prefer the acrylic smells to smells.

Andy

You need to let your Future cure for days...not hours. Acrylics are slow to out-gas and covering them before they have finished will result in a ruined paint job. Leave it shiny for a week or so then go back and dull it down if you need to.

The Polly flats are good as well as some of the other satin and flat clear coats (fixitives) used by artists and draftsmen...check you craft store. 

To amplify what Jerry said: Acrylics are slow to outgas because they have a peculiar curing curve. Initial cure is relatively rapid, but full cure can take days—and until curing is essentially complete, they are still outgassing. After a few hours it looks and feels cured—tack free—but it isn't. Future in particular is problematic in this regard because it forms a much thicker film than most acrylic coatings, and is formulated to behave this way.

You can greatly speed up the cure by using mild, forced air heat once the surface is tack-free. I use a forced air food desicator, but you can do the same with the old "light bulb, fan, and box trick." An hour or two and it should be fully cured. 

HawkeyeHobbies wrote:

You need to let your Future cure for days...not hours.

There may also be one's local climate to consider.

I live in Southern California which is usually warm and dry.  When I've been in a hurry or had some sort of deadline, I've painted a multi color camo scheme in the morning, applied the gloss coat in early afternoon, applied decals in late afternoon, and finished with flat coat(s) and weathering in the evening. To be sure, I normally give more time, i.e. several hours to over-night between any of those steps.  However, when I have used such an accelerated schedule, and it didn't matter if I painted with any combination of acrylics, enamel, and/or Testor's lacquer base clear finishes, I had no problems with the finish, nor have any problems ever cropped up years later.

For one living in Wisconsin or a similar climate, letting Future cure for anything less than several days might be an invitation to disaster.  Never having lived in a cold or humid climate, I can't say.  For me living in Southern California, letting a coat of paint or clear finish cure for anything longer than overnight is simply a waste of time. 

Andy