If you paint only the inside go with a spray can, we don't see it too much, I will say an other thing if it was the outside, since you want it flat, get a flat black primer, ( if it's only metal take anyone, if you have plastic , make sure it's compatible ) just make sure to clean the part with a good degreaser before, you can buy it a Canadian tire, or best go in a Car paint shop, the guy will sell you few and give you some tips.
