Thank you for your post.
When I touched the fins on the back of the F112, I did't feel them warm. But I do't remember well. I will see how warm it could get without the backpack.
I remember readig somewhere some peaple are putting an amplifier on top of a sub and I thought it woudn't be a problem to leave a small thing like a backpack on it.
There is one thing I am a bit concerned with. The noise level. I usually set volume level at around 2 o'clock...