Those of you who are using a wedge shaped cushion, I assume you're sitting on the cushion and not behind your back, and is the large part of the wedge under your knees or under your butt?
I have one of those vehicle cushions that fit the seat and up the back of the chair that has 3 electric vibrators in the back side near the tail bone, another at the small of the back, and one at the shoulders.
It seems my rear starts to feel sore and achy after 3-4 hours and this vibrator (plugs into the cigarette lighter) works wonders on it. I have a 2004 DP with leather seats and it seems they are very comfortable for the first couple of hours, and I do try to stop every 2-3 hours but sometimes the rest areas just don't appear in the right places.