Aye, I've done several. Closed cell foam (as suggested already) is the way to go. I used 8mm stuff - get it by the 8x4 foot sheet from a 'chemical converter'. You may need to experiment with the various glue types available. Some of the aerosols don't tolerate high temps and will crack and drop the foam on your head in the summer (dont ask how I know). The most reliable method I've found is EvoStik - they do a white low-VOC version which will ensure you dont get brain damage when sticking it in. If your roof is off and you can do it the right way up (ie upside down) then it makes life easier. (Whatever you do dont use open cell foam, its a moisture-absorbing smelly mess that will result). I've then stuck cheap nylon automotive carpet over the top. Warm, quiet, pretty.