My dealer wanted to sell me permanent rust protection, but I read that this treatment is not recommended and even to be avoided (as per the CAA and the APA). The dealer added that if we did rustproofing elsewhere, and it involved drilling holes, our warranty would be voided. Was he talking about the "bumper to bumper" warranty? I always go to Metropolitan Rust Proofing, but the APA recommends Krown. What do you think?