Was your 45 minute heat soak with the hood shut? That big V8 has a LOT of thermal energy and with a closed hood it has nowhere to go............. except into the carb.
Regardless, I guarantee you the carb would get way hotter without that thermal spacer.
FWIW, when I park my hot truck (with carb insulator) outside, there's always enough breeze to keep the carb on my L6 from perc'ing the fuel in the bowl. When I park my truck in the garage I always open the hood and sometimes even put a small fan blowing at the carb. The worst is 'winter blend' fuel that has a relatively high vapor pressure.