How do we write a vehicle allowance policy?

Q. We have employees that travel across the country to build retail stores for our client. They drive their own vehicles and we pay them a weekly vehicle allowance in addition to their salary. It’s taxable income to them, but I need help writing a vehicle allowance policy. Our allowance covers wear and tear for their vehicle and we also provide a fuel card for job-related fuel only. Is there a policy out there somewhere that you could point me too? And are there any legalities that we need to be aware of with this? – Kim, Virginia