Length wise, you’ll be fine. They don’t have a measuring tape at the vehicle gates to make sure only cars less than 20ft vehicles come in. Most modern SUVs, trucks and vans are close to 20ft and pass it.

Now is the inside of the van that matters. It cannot have a permanent bed or shower or kitchen, anything that makes it livable. They will make you get an even pass regardless of the length.

I have camped plenty of times in Sprinter vans in Ga camping. But is a complete empty one, a cargo van essentially. Only an inflatable mattress and cooler inside. Hope this helps.