Dave,
This is a tricky one really. The BARF is painted in the mold is it not? If it is, there may not be a clear coat on it, I don't know the process that BVM uses for painting their ARF's. Try sanding an inconspicuous area on the jet with some 800 grit paper, if you see any color on the paper, there is no clear coat.
If that is the case, then you are going to have a tough time getting a perfect finish since you'll actually be scuffing the color coat.

To prep the entire surface though, the safest method is going to be to simply use a grey scotchbrite pad to dull the entire surface.

So what you want to do is:

1. Wash the airplane with hot water and tide laundry detergent (the powdered variety, not liquid). Tide will cut the mold release, finger oils etc and does not have an oily residue or perfume's that will contaminate the surface.

2. Wipe the model down with a degreasing agent like PPG's DX320.

3. Start rubbing down the model with a grey scotchbrite pad. The beauty of these pads is they will not cut into the paint like sandpaper will. You run a much lower risk of sanding through colors, markings etc. Rub it down until it is a flat finish overall, you don't want to see shiny spots anymore.

4. Wash the model down repeating steps 1 and 2. When you dry the model incidently, use a clean lint free paper towel, or a clean microfiber (better option)

5. Make sure the DX320 is completely dry and evaporated, then apply your promark decals. If possible, wear latex gloves during this process to keep skin oils off of the model, and be sure to work on a clean dry surface.

6. Once done applying your markings, wipe the model with the DX320 again. Again, try a test piece first to make sure the DX320 does not affect the dry transfers.

7. Wipe the model with a clean tack cloth and apply your clear coat. Apply one light dust coat first to seal everything, let that flash off completely, then you can apply a flow coat of clear.


Note: when you apply the DX320, you want to use one clean cloth to wipe the model down, and a 2nd clean dry cloth to wipe it off again. Don't let it just sit there until it all evaporates.

Note 2: Make sure to use a dust coat of clear for your first coat, this will reduce the risk or product incompatibility with either the factory finish or the dry transfer markings.