What is too long to get into State/National Parks?

Make up your mind on what is important to you. No, you can't have the monster trailer & find a site wherever you please.

Stay under 30' & go wherever you like. Lots of sites.

30-35' the number of suitable sites starts to get fewer.

35-40, you are on a rapidly decending slope with sites getting tougher to find with every foot of length.