Easiest if you have multiple vehicles so you can declare that one is used 100% for business purposes. It gets more complicated if you use it for personal and business purposes as then you need to maintain a log and keep track of when it is used for business and what percentage of the time.
There is another aspect worth exploring. The IRS allows a per diem expense for food and lodging by zip code and for example in Orange County, CA it is a total of $203 a day. You can take that deduction while on business and stay at a RV park or campground and fixing your own meals inside the camper.
You need real business income in the first place and cannot expense more than you produce in profit. We have a business where we make sales calls that would otherwise be too expensive to make if we flew into an airport, rented a car, ate at restaurants and stayed at hotels.
A good CPA can provide the information you need and keep you from being audited by the IRS. There are perfectly legal ways to avoid paying taxes as Mitt Romney has amply demonstrated so do not simply roll over for fear of an audit. I have been filing personal and business tax returns for more than 45 years and had only one audit and it was a random audit and not one generated by a return that was submitted.
