The ONLY reason why not to solder where vibration could be a factor is because of ACID FLUXES in the solder that weaken the joints ability to flex.
PROPER crimped connectors do NOT come undone, under normal pressure/use.
F1 teams crimp and X RAY thier connections.
NO "high resistance through a car body", but at each END of the car body where you will find CONNECTORS at the battery in the loom at relays etc you WILL find high resistance, and especially when areas are used subject to water/corrosion.
tabetha