Start a blog to promote the book and supplement the limited amount of media content you'll be able to put in the book itself. Have a business plan ready to show how much you expect to make from each aspect of the business and how the blog is a vital part of your marketing plan.
As long as you actually do write the book, publish it and make more money than the write offs for the trip I don't see a problem with your plan. The key will be to show that these trip expenses were necessary to justify the earning of said income. If you never end up writing the book or if it doesn't make a reasonable amount of money relative to the costs you are writing off you may have a problem with the taxman.
I've done lots of remote work while travelling across US and Mexico, but the only part of the trips I would write off against my consulting business were hotel rooms when I stayed at places with wifi and desks so I could work vs. camping.
If you already had a book written you could use the trip as a publicity tour to promote the book in each destination and then write off the travel costs. If you like moto touring that could be a future trip.
The other thing that comes to mind is being a sales/product rep and using the trip to meet with dealers/customers for whatever you are selling [similar to a book publicity tour]. However, you'd need to be able to earn an income from this activity that was reasonably expected to be greater than the costs you want to write off.
