I have a 2000 Avalon that I need to replace the rear deck woofer speaker…I removed four mounting bolts and still need to do more removal of stuff since it won’t fit through opening hole…what would be the next thing to remove without cutting something out ?
Normally they set into the deck from above - very easy to put in during assembly with no windows and stuff in the way. Much harder now 
Since I’m not familiar with replacing an Avalon sub, this is just generic…
If your 3rd brake light in in the rear windows, disconnect the third brake light electrical connection in the trunk. It may have a protective cover, which you will have to locate and remove.
Remove the headrests. Remove the rear seat cushion(s). If you have to remove the lower cushions to do it (very often you don’t), then take those out first.
Remove the deck cover. It’s typically of a fairly solid cardboard type material, but be careful not to bend it too much, or it will “kink”. There should be a few clips holding it down, and if you have a LATCH system in the car, or a third shoulder belt, those will have to be unbolted.
Reverse to install.
HTH
Chase
Thanks…I thought perhaps that was my only way to do it…so wish me luck…I’ll start taking major things out…(seat back and such)…I have the time, so that’s not a problem…
It’s not difficult, and can be done (out, replace speaker, back in) in under two hours for someone who’s never done it before. Just a tiny bit of mechanical aptitude, and you can do it, too.