There's a product called armaflex. It comes in sheets. It's used in the refrigeration world for doing what you want to do. Once you insulate the tank and with -20 F glycol flowing through the coil. The coil might ice up. Unless, the beer is high octane. The coil that the company provides has a moderate pressure drop. You may need a higher volume pump. If the pumps is direct drive, a pressure actuated bypass or at the least a ball valve would be good to install between the discharge and suction. Low temp pumps usually have different seals and are insulated. You may want to thin down the glycol, like the other brewer did. In -20 to -40 F low temp industrial chillers, it isn't recommended to run 100% glycol. Heat transfer is less using 100% glycol. A fermenter that can be pulled down to 30's F is usually jacketed. They're designed in such away that the coolant temp is very close to the desired temp of the beer. Having a close TD keeps the beer from freezing on the tank wall. A circ pump is used to keep the beer moving, to transfer its heat to the jacket and evenly cool the beer. You may want to consider using a pump to circ the beer around the tank, especially with -20 coolant temps. You might want to get rid of the box 90's and use longer radius 90s. Or, bend up soft copper into sweep 90's and fit them to the stainless. Less pressure drop. The fermenter you have is a great investment and once you work out the cooling bugs. It will be a very valuable tool in your brewing world. The spunding valve and CO2 port are great...I have two 14.5 G stainless conicals with a blow off and spunding valve. I use CO2 to transfer from primary to secondary to the keg. No more using gravity or worrying about head space, air or micro bugs getting sucked in.