"walk-up" campsites

Welcome Gale! Here in the west, and sounds like there too, "walk-in" is only that. And "walk-up" is "first come first served" (FCFS). I've done both, different situations. For FCFS sites, which I've used many times but NOT with a trailer, I would leave my trailer parked elsewhere if driving into the campground to secure a site or driving to a campground office which many state parks have, for same. Meaning, not hauling the trailer into tight spaces if I wasn't guaranteed a site. If you do get a FCFS site, they'll give you a tag or something to indicate it's yours and you can also leave a camp chair in the site (I secure ours with bike locks when they're the only thing in the site). That way if you don't get one of the sites, you can leave more easily. And all of that said, some State Park CGs are really spacious and it might be possible to drive through WITH your trailer as part of checking for a site. Get there really early and if it's a campground office, you can sit in line in your camp chair and drink your own coffee or tea while you're waiting. I hope this helps, or at least is food for thought. Have fun and I hope you are able to get a site!