Nationals work well in our area Most european beekeepers use the bigger langstroth's but in Scotland any beekeeper I have know who have tried them say they are a bit too big for our type of bee and conditions The cold is generally not a problem for bees but the damp conditions are. I had colonies survive over the the last few winters with open mesh floors. I have also used National polyhives which also work well and give a bit better insulation. The main thing is to get your bees in the right conditions to overwinter eg colony strengh, plenty of stores and good disease control. I also agree with Jon on just using 7-8 frames with dummy boards and adding more frames as required