Yes, I have the factory insullation but the passenger side still began to discolor at 30K. At 40K I removed the passenger side, painted the inside with silver heat reflective paint, repainted the outside and it lasted about 60K.
Now, with the new one from this guy in Texas (9999evad) I used oven paint on the inside. Waiting to see how long it lasts. I don't recall if I put the factory insulation back in this time.
Oddly enough the driver's side is just now starting to crack the paint and that's after 125,000 miles. Passenger side probably has a faulty cat. I'll swap them for high flows someday.
Get a spare set of sills and painting won't be any big deal.