I've never primed a cockpit in my life, as such; I usually start by making sure the surface is clean, then just brushing on a layer of whatever color is my basecoat, and go on from there with washes, drybrushing and detail painting.
Of course, I rarely do primer externally either, unless there are light colors involved, special finishes (like automotive finishes or metallics), or I've done a lot of puttying or re-engineeing. I use mainly Tamiya acrylics...which don't seem to have many adhesion issues or problems...so the primer (to me) mostly seems like wasted time and paint.
Just my