Discretization for an object with largely varying dimensions

Hello! So my simulation is for a Philippine jeepney, where the walls of the vehicle are metal sheets. I already use the value for that of the chassis (which is quite thick relative to the rest of the sheets), and it is at an approximated value of 4.8 mm. Now, relative to the engine, which is at a modeled size of 1050 x 1050 x 800 mm, the thickness is really small. Moreover, this is also really small relative to the domain, which I got from ERCOFTAC guidelines, which is at 8L X 1L X 2L, for which my current L = 5600 mm.

If I discretize with respect to the metal sheet thickness, I would get too many lattice nodes, but if I go with a coarse grid, the walls disappear (as my initial simulations have been showing just the engine).

What could be a good workaround for this?

I’m making use of the externalFlowAroundObstacle as my current base code, if this info helps.

Thank you for your time.