Size does matter!....unless you're insistent on National Parks campgrounds you won't have too much problems. California is unique in that a 40'+ will not fit. The issue is not the site itself but rather the road(s) leading into and around the park. They place large boulders along the side of the road, and those big rocks are about compartment height. Most have rubber or scrapes on them...:E. California does have a downloadable map of all State campgrounds with length limits posted. They are not completely accurate but a simple phone call to the park will answer that question.
As for special requirements and road restrictions, California again has some highways that carry restrictions such as Hwy 1 along the coast, and it is enforced. There are several also in San Diego county that I know of. Another is Hwy 49 which runs through the Gold Country. That said, those restrictions are for coaches LARGER than 40 feet so if you're listed at 40 or less, you'll be ok. It's not that they don't like the larger coaches but rather it's for your safety and others using the roads. If you've traveled Hwy 1 and/or 49 you'd know what I mean. I wish other states would follow California's lead and post those roads we shouldn't be on. Hwy 89A around Sedona Arizona is one that comes to mind. Also there's Yarnell hill outside Prescott and the road through Jerome. I really don't like surprises as I found leaving Hawks Nest State Park in West Virginia on US 60. I'm not sure that hwy is suited for anything over 30'....:B.
You did ask for opinions and mine is to go for the 40', but do check the CCC, so you won't be disappointed......Dennis