The stuffing in the box would be polyfill.....and you really shouldn't use it in ported boxes. It's made as a last ditch effort for sealed boxes that need to be a little bigger, and when building a new box isn't an option. Polyfill would throw off the volume of a ported box, and thus have an adverse effect on your output.
I would try to get the PVC bent professionally before taking any risks yourself. I would just call a plumber or a contractor who specializes in those man-made ponds rich people get in their backyards. Tell them what you need, and if they can't do it they should be able to direct you to someone who can.
Good luck, btw.
"The world is full of people who want nothing short of perfect,
but settle for less, blinded by their quest for purpose."