Let your passion in life earn you money. Or, save you money. At the very least, combine it with RVing to cut your hobby expenses. Make the most of gathering with others who share your interest.
What are you passionate about? I'm guessing there's a club or organization about it. Most pastimes have official associations. Those associations host get-togethers, seminars, and rallies. The scope of the gatherings vary from educational to purely social. But, whatever the focus, they amount to a bunch of like minded people coming together to share about a common topic.
Those gatherings can provide free or low cost parking for RVers. The events are at fairgrounds, race tracks, hay fields, parking lots, civic centers, designated show grounds, and other locations. Some of them have a campground with full hookups as part of the facility. At others, the RVing sites are makeshift, with dry camping. You can save a lot if you don't need to pay the full nightly rate for an RV site.
Besides using it to save on camping fees, you can use your passion in life as a money maker. Share your knowledge and teach it. Present a seminar or workshop when attending those gatherings. Sell products related to it. Many of those events have vendor areas.
Most organizations depend on volunteers to make the events go smoothly. Campgrounds aren't the only place where RVers can trade time worked for a no-pay camping site. And, as when volunteer work at campgrounds, you often receive other perks, things that non-volunteers pay for.
You can use these ideas for most any of your life passions. Radio controlled cars. Wood carving. Genealogy. Bird watching. Home schooling. Photography. Quilting. Cowboy poetry. The list could go on and on.
How do you find the events? If it's your passion, you are probably already a member of state or national organizations. Take advantage of them. If you aren't a member, consider joining. Special interest magazines are another good resource. Or, be the leader and organize an event.