April is a busy time in Moab and Zion. It's the perfect weather and everybody knows it. You might find reservations tough to get at the more desirable CG's. Bryce can still be cool with even occasional snow showers in early to mid April, just depending on the year. At least Jeep Safari week in Moab is at the end of March this year, so that shouldn't be a problem for you. I usually try to get a couple of weeks of camping at Moab in April and May.