Although general wisdom decries cement (actually, I think concrete, but I'm not sure of the difference) blocks, I've used them for decades to support generations of my boat trailers (and the boat on them). But (and this might help) I never rest the narrrow metal of the trailer (nor should you rest any of your car's metal parts) directly on the blocks. I always have a stout wooden board on top of the blocks, between the trailer's metal and the blocks like a sandwich or a cushion, for two reasons:
1) I've convinced that the board spreads the load so that a metal edge doesn't tend to concentrate the forces at one spot and split the blocks (like a knife cutting into something).
2) I never want the block to scrape against the metal, to rub off the galvanizing (of my boat trailers) or (in your case) the paint and galvanizing of some metal part of your car! The cement blocks are too rough, with quartz crystals that will easily scrape off the protective finish, even on the undersides.