Well applying a clear coat is good in giving protection to the paint. Many like it that way.
As for me however, as long as the paint has set and cured fully, I just apply the wash without the clear coat. This takes away the need for a dull coat later. (I am very inexperienced when it comes to dullcoating that's why I don't like to do it.)
Before you apply a wash, decide first as to what type of weathering you want to simulate, light and subtle or heavy and beat-up. This will also be the basis on the thickness of the wash you need to mix.
Before the wash also try to simulate paint chipping by say using a gun metal paint on a very pointed brush on some areas where chipping is likely to occur. When you apply the wash it will soak the gun metal paint and makes it really look good.
If you like, you can add some rust colored paint on items that are likely to rust (mufflers, bolts, weld seams, etc.)
At first I don't like heavy weathering but when I tried my first one...I told myself..well it doesn't look bad afterall. Here is a sample of a beat up vehicle I did. (Nevermind the figures...they were among my first try and not properly shaded. Also they are too glossy.)
