Many manufacturers switched to soy-based wiring in the early 2000s, but in truth there is very little evidence to suggest that this change in the composition of wiring makes it more appetising to rodents - it is more that the engine bay and other nooks and crannies of vehicles are attractive to rodents and they will happily gnaw on anything they can. You could change your car but it is unlikely to reduce the likelihood of further issues. We would suggest using traps around your vehicle to prevent further intrusion and use repellant sprays around the wiring.