Have tried that - they seem to come back for more and it blows around the engine. I have two rat traps - the wood and spring kind but they seem to avoid them - these spanish rats are very clever ......my dogs chase them up olive trees and usually I have to climb up and rescue the dog !!! You can see the action here https://youtu.be/Q2SURpmUltk
I'd try a couple of bait boxes - something like these
The main secret to getting them under control from my mates experience (they used to get in his loft at his house) was to put the bait down, and leave it alone - they won't usually go anywhere near stuff that you've disturbed recently. He tired the traps, tried shooting them with an air rifle, neither approach worked. The buggers even managed to strip all the insulation off about 6 ft of the lighting ring main buried in the ceiling without suffering any ill effects, but the poison did actually work. If the area under the car is clear, I'd stick a bait box where you usually park it on the ground - if its really dusty there, then get the blocks that push onto the retaining rods (the ones in that listing for example are the type I mean) as you can always tip the dust out of it latter when you come to refill it.