National Parks seem to mostly have a 34 or 35 foot limit. Remember most of these campgrounds were built between 1930 and the 1950's. We have never been asked how long our 5ver is when checking in but reserve america/recreation.gov asks when you make a reservation. If you fit into the spot, then you'll be fine. If you don't they will not move you to a different spot and will not issue a refund.
That's the reason that we limited our search to 5vers 34ft or less when we bought ours. Lassen is one place where length would not matter. Yosemite would be critical on the other hand. You can find photos of the sites on some of these CG which will give more info to work with.
Some Florida State Parks would be a problem and some would not, it depends on the age of the park. Roads would be a real problem in many of them.
One other factor: how petty and officious the park rangers/cg hosts want to be. Most are fine but you will run into Barney Fife types that will harass over every petty thing they can find. Like your camper extending past the paved area for example. We ran into those at the North Rim once and at Lassen. The Lassen problem was caused by one of the campers complaining that we ran our generator during generator hours (at 4 PM for example). She finally left and the host was fine after that.
