Battery charger - connect negative to chassis

I have read, and followed the advice, that when you hook up a charger to the engine battery, you should connect the negative cable to something connected to the chassis. However, with this motor home I have a very small access door to the engine compartment that my head won't fit through to let me see some possible connection points. Will it truly hurt anything to connect to the negative post on the battery?
2018 Coachmen Mirada.