Lyn, one thing I might try if I lived in your climate is to plant all of these mail order heuchera in one big container with soil that doesn't dry out quickly. I would make a potting mix that's compost-based, and not peat-based, so that it's not so hard to re-hydrate once it does dry out. For the drainage component, I would add perlite and/or pine bark fines.
Planting all of them in one big container would make it less likely to dry out and easier to water. I would place the entire container under a patio umbrella.
I don't think overwintering them would be an issue for you, either in the ground or in containers.
