[BigDan3131]

I took the tank out of my 65 and those cab corners should be a good place to high mount a pair of new 6x9's I had left over from another project. I undercoated the whole inside of the cab then I bought a new cap and seal for the gas filler and will be using the 3M Windo Weld to mount it permanently. If I fill the cavity with Polyfill stuffing will my sound quality improve?
I plan to use a shallow mount 8" sub I have and I'm wondering if there would be any issues having an amp and remote controlled head unit mounted closely together with the sub? I was planning to mount the head unit on a fold down ramp to access it if needed otherwise it would be hidden. Should I add a couple small fans behind it to keep it cool?
How is the sound quality of speakers mounted under the dash firing downward, I'm trying to keep things as less obstructed as possible.