[Richard]

IMO, it needs to be in cab or if under hood in an enclosure. My ECM will be under dash with harness through clutch hole. If vehicle is for show only or never driven in the rain, put it anywhere you want to. Never have seen an ecu exposed to the elements under hood in any OEM vehicle. Manufactures will not spend a penny on anything that is not necessary. To each their own if you just put it under hood with no protection.