MS & MX are aluminum body so no need for rust proofing. Just picked up my M3 which is predominantly steel body with some aluminum. I plan on keeping my M3 for at least 20 years (I have a history of doing so with ICE so this EV should last well beyond that). My main concern is rust and living in Toronto, Ontario, Canada, the roads are heavily salted in winters. I've used KROWN rust control for many years and found them to be the best. My Toronto Tesla Service Ctr. rep stated not to rust proof due to potential for rust proofing solution to enter into the battery compartment. I would have thought the battery compartment would be completely sealed to prevent this. Looking for a second opinion from TMC contributors. I'll also be asking for 2nd opinion from Tesla. PS. Love my M3. Edit: KROWN is quite extensive. First visit has them drilling the car full of holes and filling with plugs in the quarter panels, wheel wells and other rust prone areas which allows their product to reach all areas of the car body.