I am assuming you are going to can primer it as if you had an air compressor you would paint it too, right?
In this case, autozone carries duplicolor "high fill primer" in red and grey. It is hands down one of the best can primers I had yet seen. Sort of a brownish/grey can. Nothing else even comes close to the fill of this stuff and it has excellent coverage and fills scratches very easy. Sands pretty well too. Leave it overnight to dry though before you sand it.
As for application, you need to clean the surface with a paint prep degreaser then cut the surface to 400 grit and dont touch it with bare hands or you will lay down finger oils that will contaminate things. Then you sand the primer with 600 grit until imperfections are covered.
But you cannot leave it like this for any length of time outside as primer is pourus and will apbsorb moisture and oils and everything. So you would prep it then drive it directly to the paint shop for the actual coating.