I painted my freezer of my fridge with chalkboard paint. I sanded the area thoroughly to try and take down the texture, then used probably 15 coats of paint, (apply, wait 2 hrs, apply, wait, apply, wait, apply wait....). I wetsanded it every 5 coats or so. Worked great, super smooth, but if I were to do it again I'd probably use a super thick primer or bondo first, sand that, THEN apply chalkboard paint, (probably would have reduced the # of coats by quite a few!). I used "adhesion promoter" primer, which is a spray paint can full of solvents and a primer that is a primer in the true sense, (little-to-no thickness).
So, sand it down, Prime it good and wet sand, then apply chalkboard paint, or sand, bondo, sand, paint, or sand, paintpaintpaintpaintpaintpaintpaint-wetsand (repeat 2x).