The problem I have is three piece belts feel great with 50 lbs, but with packout loads of 70-110lbs the lumbar pad slides down my back and the belt digs into my hips in a bad way.
Barbell squats, heavy ones, might be the answer for you, rather than another piece of kit. Developing your glutes, or "growing an ass" will give the belt somewhere to sit. Find a coach, and or buy Rippetoe's book, Starting Strength.
