I've been lurking for some time and my apologies if this question has been answered elsewhere.
My family (myself, wife, and 10 year old son) will be traveling clockwise around the US next spring, starting in Vermont. We'll be travelling mostly on two lane roads with pickup and rented popup trailer. We have five weeks and most of our time will be spent in the western national parks. (We'll head north from Tuscon missing unfortunately the west coast.)
My question: do we need to reserve campground spaces at the national parks in advance? For example, I'd like to stay in the north rim campground at the Grand Canyon. If we arrive mid-May, do we need a reservation? The challenge is that I'm not sure if we'll arrive on the 8th or the 12th of May and I'd rather not lock into a schedule. The same is true for all the "major" western parks: Yosemite, Grand Teton, Yellowstone.
Thank you for your advice!