I agree, a constant 40A current draw will get relay terminals warm or possibly to hot to touch. Many GM Fan Relays are 0.125" terminals. The relays selected are 0.250" terminals. The box was built...

Pictured below is a 40 Amp Fan Relay Module - Dual Speed

Build Details below.

https://catalog.waytekwire.com/Waytek-2020-Catalog-232/179/

Fan wires are 10 AWG
Primary Ground wire is 8 AWG...