Not on a PC (still not retired, so no 4x4 PC or Provan Tiger, yet), but the issue is valid for any vehicle: The shop doing the lube, oil, filter, and inspection of Dad's '97 Dodge Roadtrek 170 discovered deep weather-checking (cracks) on the sidewalls facing inwards (the side facing center of vehicle). None were on the sides facing outwards, where one would expect sun damage. I wondered if there was more heat from brakes on that side; the shop owner said if there was enough of a difference to do that, everything would be damaged. The only other thing I can think of is that the yearly vehicle polishing/waxing by a local car wash that also included application of Armor All or something to the outward-facing sidewalls (the side one sees) saved them despite sunlight hitting them while the shaded inward-facing sidewalls aged normally due to oxidation. These are Michelin LTX P235/75R-15XL, 8 years old and hardly worn with 40,000 miles, but now obviously due for replacement.
Bottom line? Clean and treat both the inward and outward-facing sidewalls, and keep an eye on 'em. I'd imagine a household refrigerator coil cleaning brush, or similar bottle brush, would get between your duals.
