Kaowool is great stuff, cheap and easy to work with. The dust off kaowool is dangerous, if you put it on the outside of the roaster cover it with something, maybe aluminum flashing.
I may do this to my HT this winter. If I do I'll use foil and fiberglass duct insulation . It comes in 12" wide rolls and is easy to work with.I'd also get the foil-backed tape to seal it.
I wanted something that was not bulky/thick. I also think that minimal insulation will work nicely as a towel can change a roast profile especially if it blocksthe upper filter - (note that this is a HUGE fire hazard that I do not recommend trying). Tex - That tape looks good too. Will the glue underside of the tape withstand the heat of the roaster if its used at the border of the insulation and metal HotTop roaster siding?