My project involves using around 8 accelerometers to measure multiple aspects of a motorcycles attitude while racing.
Having longer I2C or SPI buses in such a noisy environment won't work (I would expect a bus length of more than 2m given the places you mentioned). I'd suggest to partner every MPU with a small MCU (p.e. an ATtiny) which then communicates with the master by a CAN bus (which was developed with such environments in mind).