My understanding is that you can overwinter a Mandevilla in warmer regions, but I tried it in Ohio and, even though I brought it into the house, it failed. I don't know about using the bare-root process. You might look at one of the forums with gardeners in the southern states. If anyone would know, they would. Good luck!
Thank you , belated, I just saw this. I gave a mandevilla to a Mennonite nursery and they managed to keep it alive . It grew around the front part of the shop witch had lots of sun. And was part of a green house.