Mine are in the ground, so they stay there. Only when
frost is suspected do I do anything, which is try to
cover them. It's getting almost impossible because they're
so darn big.

Two years ago when we had freezing temps, I covered each
growing tip with a sock until I ran out of them. Now I
have many more growing tips than socks.

Are yours in pots? If so, when there is a chance of frost
or freezing temps, stash them somewhere under cover.

Not doing much watering as of late. Since most of the
leaves will be falling soon, I don't worry about watering.
They're going dormant about now anyway.

Should I water at all while the plumerias are in dormancy? Mine are in pots. I like the sock idea! I am a plumeria newbie too; thanks Matt for asking this question as I have been wondering the same thing.

I live in Costa Mesa and have about 35 large plants in the ground and several hundred in pots of various sizes. Mine stay out all year and with thousands of tips, I cannot cover them. I have only lost a few plants during rare hard freezes and the last was in 2007. I rarely water in the winter, only if we have a Santa Ana condition. No leaves = no water. These plants are from the Caribbean where long droughts occur during the winter. Bringing pots under a patio cover or a porch will decrease damage from cold. You can also give your plants Armour Kote or Pro-tekt which contain potassium silicate which protects the plant from stress of cold or heat. I put this in my last waterings of the year because I do not have heat problems here.