Before you spray the primer on the interior, be sure to sand the metal with 180 grit to get a good bite on the metal. This is important for when you remove the masking tape off of the interior after you paint the exterior. If you don't, you will risk pulling off the interior paint when you remove the tape.
You will likely be sanding the interior primer before you paint with color. This is also important for the same reason as above.
Don't ask me how I know this.
