How is air blowing on the PC. The vents have ducts that go straight to them... maybe its ducts are getting hot and the inside of the dash is getting hot through radiant heat. If thats the case you can always try to insulate the ductwork. which may be difficult. Think of exposed duct work in department stores that have what seem to be blanketed. Thats so that the hot/cold air generated at the HVAC unit is still roughly that same temp at the diffusers or vents.
Another option, get longer connects and relocated the pc to an area that you can more easily control the environment e.g. under the seat, in the center console, in the trunk. I'd go with relocating.