We've stayed at both Lee's Ferry campground and Lone Rock dry camping area both part of the Glen Canyon Nat'l Rec area. Here's the link for camping info, maps and things to do:
Camping - Glen Canyon National Recreation Area (U.S. National Park Service)
Lee's Ferry is dry camping but has designated sites. It's on a bluff overlooking the Colorado River. Lone Rock has no designated sites and is on Lake Powell. It would be the closest to the town of Page. At Lone Rock we prefer the area just past the entrance station on the left. It's on a bluff overlooking the lake. If you drive down below to the beach camping area be aware that there are some areas with soft sand. Pick your spot carefully.
Escalante has a good web site similar to Glen Canyon's with camping information. There is a lot of open land in the gorgeous area and all is accesses via Hwy 12 and there's a office in the tiny town of Escalante.
May is starting to get hot in the Page area but cooler at Escalante. Have a great trip. It's a favorite area of ours.