I don't know the car either but I can confirm that while Port Huron does have a little longer winters (due to the lake effect snows) they are not that much longer than Detroit. Port Huron is about 45 minutes to an hour north of Detroit area off I94 and while they do have a number of gravel roads the majority are paved.
I would actually expect the over all condition of the roads to be worse in Wayne county (Detroit). Even with close to 100% paved they are in such poor condition you may think your in a third world country. Think of Detroit as the armpit (or worse) of the nation!
My car came out of storage on April 1st and I should be able to drive it until the end of November. The temp here today is going to be about 70. Even with the long winter there is still ample opportunity to put miles on your car.