Definitely use Etching Primer per the instructions.
Clean the box with soap and water.
Sand with 200 grit paper or finer if you want,(sanding alum is a PITA).
Wipe down with PrepSol or other pre-painting solution.
Spray the Etching Primer and let dry per instructions.
Spray on Top Coat - two or three coats but not all at once, one coat one way then the next coat the other. Slight drying time in between each coat.
AND ALWAYS use the same manufacturer’s products on the entire project.
DuPont make a good etching primer and IMHO they make great paint for the general public.
4x4, 5sp, Std Cab, Stepside, E4 Red
4” Lift - Coil-Overs, 6” SkyJacker Leafs - No Blocks (Mistake)
31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter