It's getting cool now, even for your zone.
I find the best way to dissolve sugar is to bring it up to just when starting to boil but constant stirring until this happens, put hot water from tap first then sugar stir and put on heat.

Bees don't take it when it cools down too much, what I sometimes do is to feed in a bucket/upside down, inside a empty box over the hole in the hive cover, also put insulation around the bucket and over to keep warm or warmer from heat of the bees. [large population]

You might need to combine yours to make the winter, how large is it?
You could stack it on top of another hive with only the hive cover and screen over the hole or without hive cover, screen the whole top and put hive on top, you will have only a upper entrance which is OK. The lower hive will help to keep the smaller hive above warm. I you feel it's warm enough to open the hive, them I would put in a frame feeder, this will be best to feed bees. [warmer] I really don't like to desturb a hive this late in the season.

Use 5:3 weight, sugar to water. 4:1 will be tough to keep in solution, 2:1 can be tricky, but you need to get a really good boil on it to dissolve and keep it in solution. 5:3 works a lot better and stays in solution.

Probably a little late on this response, but look up candy boards. They are good to feed the bees in the winter.