My personal best, and not to boast, is keeping 2 mobs constantly trapped, and it was for Moroes. I had my own mob to deal with, and for our guild we normally kill 2 adds, and CC 2 adds for Moroes. Well unfortunately one of the adds got loose and killed our Shadow Priest who was shackling him. As I watched the mob quickly turn to a healer, I took it upon myself to kite him until I could get another trap out. What happened next was a series of kiting and traps. I would always have one constantly frozen, and lay another trap as soon as possible, but I didn't let the mob into the trap right away. I would kite the mob as much as possible, before I absolutely had to trap him. That way when the other one popped I already had another trap waiting for him.
Other then that, I can keep a mob trapped indefinately. I don't have any problems with keeping a single target trapped until the cows come home. Now if I put on my CC gear (2 pieces of beast-lord) I can go to sleep while I trap things =P
Before I spec'd Survival I had no problem chain trapping indefinately. The key is timing and laying your traps seperately. At most you have to wait 10 extra seconds for the cooldown. That's easy enough to do if you lay down a trap, and use a concussive shot as they come out of your first trap. Make sure your trap is far enough away, and you're set.