Prep and painting louvers & engine cover

I finally got off my butt and re-arranged my shed so I can use it as something of a paint booth, so I now effectively have the space to repaint the engine cover and louvers.

I've got to repair some large scratches in the louvers- I've got some Bondo gazing/spot putty to repair those, and have some more 'real' Bondo to fill in the holes from the old 3rd brake light.

Obviously, they will need to be cleaned heavily- what works best for paint prep?

I've seen it said to initially sand with 320 and then wet with 400, is that right?

Is it really necessary to go over them with a primer first?

I've got SEM Trim Black to repaint them with... I'll make an attempt at getting the texture of the louvers back (think Dave said to spray from further away so the paint is partially drying before hitting the louvers), but if it doesn't work I'll deal with having the smooth black.

Thanks!

On a good, non-cracked, but faded screen and cover I go over the whole thing with high grit paper lightly and distiller water then once dried as few layers of my favorite black spray.

I first had to clean all the layers of shiny protectant I applied to my Louvers with Acetone, one entire roll of paper towels, and one good pair of Nitrile rubber gloves.
Next I used lots of Denatured Alcohol and more paper towels to clean any leftover Acetone.
IF you have silicone based products on your Louvers then the paint will NOT stick.

I painted the Louver and the Engine Cover while they were hanging vertically. Be careful because they are both plastic. And the Engine Cover could crack at a week point if you press way too hard while cleaning.
I used more than one 15 oz can of SEM Trim Black on the Louvers so get plenty for everything. I did not even paint the underside of the Louvers since they looked fine it was the top surface that gets dull from the sun exposure. But, I did prep and paint both sides of the engine cover to make it look uniformly black.

I already mention what I did with the SEM Trim Black in the thread below. You’ll see it.
http://dmctalk.org/showthread.php?19...-Part-II-of-II.