Sounds like you've changed your plans. I did read that you tried to make reservations in Zion at Watchman Campground and it was full. Keep checking on line for cancelations! They happen all the time and keep checking up to the night before you arrive if you haven't been able to get a spot by then. We got 14 days with cancellations this spring but had to move 4 times! Our last night reservations was made just the night before. There are some BLM campsites not to far outside the park near Springdale, so ask at the visitor center about them.

Most first come first serve campgrounds in the national parks fill up by early afternoon. Just outside of Moab are a lot of BLM campgrounds along the Colorado River on both the Potash Road (Hwy 279) and scenic Hwy 128. I doubt you will be able to get one in Arches or Canyonlands, Island in the Sky district. If you can't find a campsite at Capitol Reef ask at the visitor center about BLM camping just outside the park.

I would recommend three nights and on full day for each Arches and Canyonlands, Island in the Sky District.

Utahtea