They will automatically list your site and give you high rankings when you have lots of content. You can create seed content yourself by writing about your trailers, your business, horses, horse experiences, tack, answers to frequently asked questions, buying guides, complimentary products, etc. Replies to customer e-mail is great seed content. By far the most powerful way to generate content is to create a community of horse lovers, trailer owners, etc. who contribute stories, expertise, articles, participate in visitor forums, etc. to your web site. You're in a great business for this.
Horse people are fanatics.
Everyone likes to see there name in print. Linking to other sites is another good way to market online. I see you have done that to a certain extent. Horse organizations have a lot of members who can provide content for you. Think globally, act locally.