If it was one that we use year round, I?d agree but it only gets pressed into service on special occasions (a few weeks over Christmas and during this Covid crisis). A new one would be a minimum of £170 and for the amount we use it, not worthwhile.
If I can find any insulation off-cuts in a skip somewhere then it won?t cost me anything (bar the glue) to have a go at improving its performance.
Tim