With the technology today, and for best product temp control, its a simple solution. Thermostat, solenoid, and defrost clock. Defrosts are totally dependent on climate, but 4 times a day, at 45 minutes apiece will ensure a 100 percent clear coil, but not warm up enough that the customer will notice. If anyone asks you to anything different, they are cutting corners, and trying to save money on the install. If you're not going to do it properly on the install, don't bother. You seem like you have the right attitude. Keep up the good work, and don't listen to the guys wanting to save the customer $10, and cutting corners.