How to paint sub box?

Hey i'm kinda new here i've been looking around and found a couple of good ideas for my 2004 Aveo.
The Aveo is my second car, my first was a cavalier but i sold it, i'm looking for some cheap mods, If you have any ideas thanks!
But as of right now i'm wondering how do you paint a sub box or did you all buy it like that?
This could be a silly question but i'm just starting to get into "fixing" up cars

Thanks

a wood box? or fiberglass? either way you need to finish it in fiberglass, to smooth it out. add more screws to the wood box to make sure it wont flex to break the fiberglass. after finishing a few layers of fiberglass and getting it smooth to about 150 grit paper, you could want a layer of filler to fill smaller imperfections and scratches. this might take 2-3 layers also, sanding in between. once you get that finished to about 320 grit, you can primer it, high build primer, not rustoleum. Then sand that with 400 grit, and prime again. wet sand that with 600. and paint with color.

If you worry about your car paint then don't worry I suggest you a better car paint, Which is that (KemFill 2K HS Urethane Primer Surfacer 1.5 Quart Kit)

Its really nice and best paint kit most of auto painters use this kit for every type of car paint its not too expensive and also have good quality of paint, No doubt there are many other paint products available in the market but it is the best kit for car painting...