Looks like a good way to go. I added some raammat to my roof when I had the truck torn apart, but I didn't really live with the truck beforehand (and the truck before it was white) so I don't know if it's helping much. One thing I noticed, though, was that the roof ribs had come unglued from the sheet metal, so I reglued those with seam sealer before putting it back together. This was more about noise than heat but worth taking a look at while you've got it open.