you can go on line and go to the national parks website, click on the link for plan your visit and when you find a park, it usually will tell you what size limitations there are. Also, find the phone number to the local park and call and find out. For us, i have been pretty successful by opening up the campground map, figure out which space is 3, 45 or 76 etc, click on google maps and zoom in and you can sometimes figure out the configuration of the spot as well. We have been all over and usually will not have a problem finding a spot, at the least, a near by state or national forest will have camping spots, local information, a camp ground host with a phone, (ins some cases) and then just do day trips to the national park if needed. Good Luck & Be Safe ! ! !