Has anyone here done it? I was thinking about building a system for my truck but figured I would check here to see if anyone has one or knows anything about how they are build and how they work. I was talking to a guy with a 07 silverado extra cab that said he doubled his MPG's but I didn't get a chance to look at his system. I have searched the web for the plans but cant find one that is detailed. I am looking for the plans and feedback from people on here that have experience with it to see if it is worth my effort or not.