There is a website EZPerDiem.com - Per Diem Tax Rates & The Per Diem Calculator for Flight Crews! that can help you with that.

They specialize in helping you calculate the authorize Per Diem of your overnights at a very reasonable price. $29.95. You will most likely make that up in your first overnight. Plus if you use the promo code C1Q4L you will get an instant 10% off that price.

As for your taxes, they have a companion website called EZCrewTax.com - Flight Crew Tax Preparation that will help you do your taxes. Again, use the code C1Q4L to get a discount.

Taxes aren't fun but these sites definitely makes it easier.

I wrote on my blog about how it works and you can visit my entry here: Get More Out of This Year's Tax Return - Almost the Speed of Sound

Good luck!