Here's a pic of the seats that I've built. VStrom on the top, XSR900 on the bottom. Stock seats are on the right, modified stock seats on the left. Both were built up using layers of the purplish rebond foam carpet underlayment.
You can't really see the full shape of the modified VStrom seat because I used one big piece of vinyl to keep the seat waterproof and simple. The vinyl stretches out a bit when you sit to conform to the underlying concave shape, but it's hard to see that in the photo. The stock VStrom seat is good for about 45 minutes, and the modified seat is good for multiple consecutive 10+ hour days.
You can see the layered buildup and shape much clearer on the XSR seat since I haven't covered it yet while I'm still testing it out. I don't think I'm even going to do vinyl on this one, I'm just going to wrap it in a black garbage bag for waterproofness and then throw my existing air-mesh cover over top. The stock XSR seat is good for about 45 minutes, and I haven't found the upper limit on the modified seat yet. It's comfortable for at least 2 hours, and I'd be super happy if it was good for 3, because the XSR can only do 250km on a tank of gas anyway.
I obviously haven't built up the XSR seat nearly as much as the VStrom seat, mostly for aesthetic reasons. The XSR is kind of pretty and I'd like to keep it that way, but there isn't much you can do to a VStrom to make it uglier, so that's ok.