Don't worry about cold nights. It can be hot, hot, hot in April. Canopy the trailer - helps insulate a bit. Loose clothes, lots of water, sun block, hats and comfortable shoes are a must.
Of course, if El Nino works out as they forecast, a canoe would also be useful...
But let's think positive here. Heavy rains can result in astounding flower displays - as well as flash floods and the rangers are always up on that, so relax, stay safe and have a blast.
I'm bugging Jim to hit the valley this spring also. Love it there.
Camp on,
Sue and Jim (the bugged one)