I am having a problem with my rear bottoming out and the tires getting chewed up by the fenders.
I've got pretty new KYB Shocks in the rear and Jamex lowering Springs.

 

Coil spring inserts are going to shift around on the springs- they suck. I ran with them on my car until I put air shocks on. It might be time to either get regular rear springs, roll the fenderlip with a baseball bat, or buy new wheels, or buy new tires. The inserts would be a temporary fix, though.

 

Like TomP said, sounds like it's time to mod the fender lips. How wide are your rear wheels?

 

Check your bump stops, see if they are still there or if they are split, the rubber are not that durable and get mutalated fairly easy, if they are bad energy suspension should have them. The fronts I know they do, the rears I'm not to sure. How often does it bottom out, if it's all the time or most of it then yeah you'll probably have to do something with the fender or get narrower tires or you could try taller bump stops, but I don't think taller bump stops would be the best fix

 

Well, I can prevent the bottoming out part of it by going really slow over little dips in the road, but the tires I believe got chewed up when I was cornering really hard, I heard the wheel rub the fender.

I am running 17x9 WS6 Wheels with Kuhmo Ecsta Supra 712's 275/40/17, with a 95 Formula Rear End.

Could my springs be bad already? They were on the car for 18 months, but the car sat in the garage for 9 of those months while I did my TPI swap.

Shocks are about 2 weeks older than the springs.