Mike O'Connell

Adding some sand is fine, but here's a couple things to consider from my experience:
If the raised beds have drainage ports at the bottom, gravity and the sun hitting the beds from all sides is going to accelerate the drying/evaporating process. If you are planting water loving veggies in the beds like tomatoes, i would want to hold as much moisture as possible without puddling.

have you tried broadcasting EPSOM salt? i did this years ago with some raised bed gardens that had slug problems. seemed to slow them down enough to let the plants develop. of course you need to reapply after rains, but nothing is easy.