The Oregon Aero, I've got the 2" seat base which is $169, plus the 2" full cushion back with the included lumbar support, another $179. That's $348..... for a seat cushion. Holy crap. It's outrageous. But after sitting on it for 5 years, it's a bargain at twice the price.
Last time I was at home I took mine out and washed it. The covers unzip and can be machine washed and dried, actually. The foam inside was kind of falling apart, but spray adhesive fixed that easy enough. But I also handwashed the foam in the bathtub with some carpet cleaner, the pet stain kind that has enzymes to remove odor (because it was starting to stink after not being washed for 5 years). I sprayed it thoroughly with the enzyme oder-killing carpet cleaner and let it sit for several hours, since it takes hours for those enzymes to work. Then I washed it in the tub with some liquid laundry detergent (Woolite would also work), and let it soak for a while, then rinsed it out, rolled out the water (don't twist it). It took about 3 days to completely dry. So for 3 days I drove the van around town without the cushions. It was just awful. It was like driving while sitting on a milking stool. Just awful.
In addition to the Oregon Aero, Espar and electronic gizmos that other have mentioned, I'll mention it again that getting the side windows tinted makes a huge difference for both comfort and safety. DOT allows CMV's to be tinted to 70% light transmittance, but for cargo vans it can ge as dark as your state allows.
Sometimes I'll even double-up and add this
Rosen Crew Shade to one of the windows. It's tempting to stick that right in front of your face on the windshield, but don't do that (even though it works great, especially out in the desert
).