I just swapped my stock muffler for a flowmaster 40 series a little over a year ago...sounds great and had no problems

 

Just because they come with clamps doesn't mean you can't have a shop tack weld all the joints! I did that with my Mustang exhaust. I put a Magnaflow set-up on and just tacked the joints so it wouldn't move at all. Then when I wanted to get up in there and do some work I just used my dremel and ground the weld bead off. I only tacked a very small spot. With a tack and clamps, it will never even move. Actually, come to think of it, I did that to my Magnaflow exhaust on my truck because the tips wanted to keep swinging down on me. This way you can remove it without a huge mess and cut off tubing.

 

Did the same with a Borla XS Pro. Clamped and tacked with a 18" piece of pipe. Sounds great and maintained the stock pipes with a stainless steal tip.

 

Just did a muffler swap on my 2006 with the AT3030. Left all stock resonators on. Sounds pretty sweet! only thing is it's very quiet at idle. I wish there was a little more rumble at idle.