For those in RTW states, I've found simply educating people as to what our union is for and why we should be supporting it goes a long way. I try to explain about insurance, production harassment, safe work equipment, and how some of these things wouldn't be here otherwise. The first words to someone that you're looking to bring in the fold shouldn't start with "You need to pay....." It should start with "Would you like to learn something".
People want to know that their money is going to do something worth while. I see no difference in the way some people handle the union sign up than the way UPS handles United Way. Think about it.