I have a new 2011 ex-l sport and I had it rust proofed at the dealer. Now they say it's good for ten yrs, but I noticed they don't drill out the main body and spray like the guys at crown rust proof do. Is rust proofing inside the body as necessary as the doors, hood, trunk and undercarriage? Do you guys think it's over kill to go get it done at crown. Thx for your help.