Lithril
Fish Addict
I'd be very surprised if your puffers could damage the pleco too much. I keep a couple with my SA's and great thing is the pleco will not interfere with anything else as long as they leave it alone, but if the puffers get too close it'll actually chase them across the tank before resuming munching.... Saying that I did see one cheeky puffer they other day steal a load of bloodworm that the pleco was actually eating... 

I keep my figure 8 in a FRESHWATER 30 gallon. And I emphysize FRESHWATER. I know a couple of people who really know what they're talking about and they keep all theirs in a freshwater tank. I hear that they can go in both. Whatever...