Yup, it's a bad idea to mount a sub upside down... The thermal circuit finally tripped (on an 80 degree day) and the system lost audio...then 10 minutes later it returned. So I had to go to Home Depo and get 4 L-shaped brackets and a piece of wood, and with a little bending of metal (the brackets that is..) The amp is now mounted upside-up.
I'll have pictures soon, once my lazy but buys a digital camera!!
Thanks guys, system sounds great now.
