I just love it when you have a particular problem that ends up being resolved by a very cheap and simple solution.
I have found that my mash tun will shift 4 to 5 degree over a 90min period if I leave it exposed or bare. But when I wrap a cheap $8 foam camping mat around it I only lose 1 degree.
Camping mats - the solution to every mash temperature problem! My insulation on my new mashtun is just foil and camping mat and it seems to work fine...