It is not near as difficult as led to believe. The IRS sets a standard per diem rate that can be used for any area in the CONUS if not wanting to take the time to determine each area visited. The rate for meals and incidental expenses (m&ie) for 2009 is $39. The rate was increased on October 1, 2009 to $46. You can chose to use the first rate for the entire year if you do not want to separate the dates. Just remember that a truck driver (as example) must subtract 1/4 a day each day leaving and returning home. So if he stays out for 5 nights he can take 4.5 x $39 for his allowance for the week. Hotel rooms, if he has to stay in one, are figured separate from meals. He can take actual or the rate for rooms. Remeber that the m&ie allowance is subject to the 50% reduction for meals, or 80% for those under DOT rules.

Each state has a rate based for meals, etc. and DOT specifications if under hours of service rules. If not, then yes, IRS has a guideline for meals while away from home.

His hotel expenses (if any) are deductible fully, but is he sleeping in his cab or he is paying for hotel/motel?

There are different per diem allowances for different places. Make a list of the places where he stayed overnight. Find the per diem amount for each place. Determine the total per diem for each place (based on records of when he was there). Add the amounts for the different places together to find the total..