Well, growing a rhody in Caribou will present some challenges. But I have seen them as far north as Waterville and they also grow in central NH where it can get quite cold. And I know people in southern Minnesota who have had some success as well. It will need to be fully protected. First thing to do in fall is to spray the leaves with wiltpruf which prevents dessication. You need to do that while temperatures are still above 40. Then, set up a chicken wire fence around the plant, fill and cover with leaves, then wrap the whole thing with burlap. You need to keep the rhody as snug as possible and totally protected from the wind. Even with that protection, the other challenge will be low temperatures. The flower buds are killed at significantly higher temperatures than the woody plant. So even if you get the plant through the winter, it might not bloom because the flower buds form the previous summer and must survive winter to bloom in the spring. So I think it is possible but you would need to find the hardiest varieties. There is a huge variability in rhododendron hardiness. You might want to travel to a nursery in southern Maine or NH (Waterville-Augusta or Concord area). They probably stock rhodys that are hardy in those areas...and then your task will be to get it to survive further north. Don't buy a rhody from southern New England (Mass, RI, or CT) or points further south. We have lots of rhodies down here and many of them would not survive further north. All that being said, you will not be able to grow a rhody into a small tree, like they do down here, but I think you could get a small plant through the winter. And it will LOVE the cooler Caribou summer. Good Luck!