I love seeing vehicles fully painted with a company's advertising. It's a great eye catcher.

Magnets...not so much. They're great for run of the mill advertising. I've used them, but have lost them to the wind too. But if you want to make a real impact, definately a full body paint job is much better.

Even though it's not a new idea, it's not an idea that has been done to death (yet). So, sure, research it, write a business plan and see if it's doable.