x2 on seal when it comes to dust. The bed has drain holes everwhere. Great without a cap, they let water out. But with a cap they suck dust in! The tailgate is the real challange. It's like Toyota's engineers never considered that someone might put a cap on the bed...... Also, probably the biggest issue is our trucks. Its a tough truck bed to seal up. Search and you will find this seems to be more the issue then any one brand out there...
Here are my dust proofing steps