My two cents,, I realize we get heat from the engine area(cowling) and so forth,,, Could the heat from the underside some how be funneling toward the seat area and super heating that area?? I know that we have talk about the carpet,,,, I hope there is a heat shield material under the carpet? Realize the seat is bracketed to the frame.
Maybe a couple of you guys on the road could do a check of the underside after you have traveled a couple of hours and see how hot that area is under the seat,,, then compare yours,,,, I'm going to go with something heating the metal and transmitting it upwards... About 125 degrees is very uncomfortable to the touch,, and with that super heat coming off the engine would not take much Keep us posted
sparky