If you're haven't been tracking your business mileage, the article in the link below might convince you:
http://www.mileagewiz.com/WhyKeepALog.aspx
The company sells a product to make it easy for users to create a mileage log. It's $39.95 annually, but you can try it for free, or contact me, and I'll customize an electronic log especially designed for your needs. Whether you travel by plane, train, or automobile, you'll be in compliance with IRS regulations.
Remember, log it or lose it.