I haven't used them personally (my safes are packed like sardine cans, even the largest ones), but most folks swear by these and they hold more guns/take up less space than turntable racks:
http://www.storemoreguns.com/gss-product-line/rifle-rods.html
I have some of the rifle rods and they work great. I does help with maxing out space in a safe.
Rifle rods, FTW.