I don't see a problem with setting a website and put adverts or a donation link. Blogs and websites are media after all. One big problem is when people pretend to raise money for a cause and keep part or all the money for themselves. Another problem is promoting your website. If you drop links all over the place without contributing, it'll be seen as spam. Yet another problem for a 4 week trip is that your tour will be over before anyone even knows about your site and you won't make a dime. It's much more efficient to save money with a "normal" job.