Don't be discouraged by the naysayers, it can be done. First check out
George's Blog He kept his mileage under 30 miles a day and rarely paid for a place to park. His tricks and advise will be very helpful. Also, since you have plenty of time, staying in one place for a week or so and exploring the area and then moving on will work. There are some on-line sites that list boondocking places and a couple of great books. Make sure you get a National passes and you'll get great discounts at National Parks and Forest campgrounds. Benchmark maps list most campgrounds
It will be super important that you keep up the maintenance on the rig and start a savings for those things that will wear out, like tires and batteries.
And lastly it will be hard, but you will have the time of your lives.