1 part epoxy primer and more primer..

Folks,

I will be putting my car on a rotisserie this spring and having it soda (or vapor) blasted to find out how deep of a hole I have dug for myself :). There is a coating they spray on it afterwards to prevent flash rusting for about 5 days.

I intend to seal the whole car with 1 part epoxy primer then get to the bodywork. Not sure how long that will take. I am hoping not more than a month or 2.

My intentions are to spray the wheel wells with truck liner (or some sort of protective spray) then spray primer, couple coats of the colour than a few of clear. This is for the underside only.. I will let a pro do the outside.

Do I need to scuff up the underside before I put on the primer if it is a couple months later ?

Can I spray clear with a 1.4 needle ? .. or do I track down a 1.3 needle.

Thanks