If you're going to spending the time and money to shoot the HOK you will want to have urethane primer on everything. The etch can go down first and then urethane over that. First do the plastic filler work and then shoot the etch, as long as the brand you use has recommendations for that. Then sand the urethane and shoot the color just like you would on the top of the truck.
If you plan on using HOK paint, just go with HOK primers.
