You have to learn to use some control when running WAY over RMS. Problem is that a single sub set up won't be loud enough to make you turn it down, so you can thermal the VC, or voltage drops and clips the sub to death.Great to know, I definitely que'd in when you mentioned that earlier. Hopefully my 12 will fair as well as your 18.
It's yet to break any kind of sweat what-so-ever playing on my BXi2100 .5 ohm load. No voice coil smell what so ever.
Now it's more of a matter of running one Kicker ZX2500 or strapping the 2 Hifonics Amps together(for roughtly 4k). I have it in a 2 cu ft box tuned to 33hz and the output is now where near its max capabilities but the excursion is pretty crazy.
Just be smart and if the sub starts getting stinky, then back it down a little...