To answer your question, you need to consider a couple things:
1. Who is your target market? (Age group, lifestyle, income bracket? where do they usually go?) That's a lot of info to take into consideration, but if you are depending on just trade shows, you are shooting blindly and hoping to hit a target that may not be there.
When you want to generate leads that you can convert into memberships, you have to start with an end in mind. How many new memberships do you need before you can break even? How many to profit? Who is generally the one paying for the membership (mom, dad, kids)? Who's looking for your campground?
There are associations and I keep telling my clients the same thing--find your association and get a membership with them to stay ahead of the curve. They are out there compiling data for you to use so you know who to target and how to get to them.
2. A normal business usually employs a few different tactics to find new leads and hopefully converts them into paying customers. Aren't you a normal business? Of course you are.
So, what you may wish to do is start looking to employ different modes of marketing to attract new customers. This doesn't mean go spend thousands of dollars to get print advertising in the paper, or even a trade magazine. However since print media has lost so much of its market, it may be a good idea to advertise in a camping magazine, or outdoor magazine of some sort. They may be having some great specials and their distribution may be just what the doctor ordered.
Look for avenues online as well. You're a campground--go green. Everyone is doing it, so market green on the internet--it works. Numbers according to the ANA (Association of National Advertisers) show that internet marketing is quickly catching up to TV (http://tinyurl.com/ananews). The difference is, unless you know the insiders run for TV, you're better off marketing online. That can be through social media marketing, email marketing or just simple advertising through a Google adwords campaign, or banner advertising.
Whatever you choose, make sure it fits your budget for advertising/marketing. If it makes sense, do it. If not, keep researching avenues until you hit a marketing campaign that gives you the most bang for your marketing dollar. Some of these can be free if you choose to run your own campaigns.
If you need to find out more about the types of marketing mentioned above, you can Google it and you will find a ton of online advertisers. Be forewarned, just because they are at the top of Google, it doesn't mean they are the best for your business. Remember that relevancy is prime when it comes to who will be helping you. If you're a do-it-yourselfer, take the time to do your due diligence, and find the right help, or research it until you are comfortable knowing what questions to ask when it is time. Until then, keep doing what you have been that has been effective, and start researching now.