Do you have of your oil cooler shutter? Was it installed onthe front side or aft?
I used to work on Boeing 737s and we used some very light weight insulation called oracoat. It is think silver mylar, and thin 1" thick fireproof insulation like spun glass. YOu make up these blanket with the mylar on each side and seal the edges with silver mylar tape. These blankets are very durable and provide excellent insulation. I bought some and used some of the scraps from work and insulated the entire cabin on my Cessna170. It was toasty warm at -20(f) but an added side benefit was it made the inside of the cabin much much quieter .It takes a little while to make up all the little angles of the different blankets but it is worth it. They are easy to clean if you get oil or dirt on them and they are very durable...They are extremely light in weight.