I didn't notice too much ice buildup around our spa last winter. A few times our cover lock tabs iced up due to water dripping on the spa and then freezing. We also got some ice on the top of the cover, which was easy enough to remove by just lifting the cover. We did have to do a lot of shoveling to reach the spa after a snowfall, but it was really worth it. Winter rocks for spa use, unless the temperature is really low and the wind is blowing. Then we chicken out.
We do have to add more water in the winter, and we do it just as you said, via toting 5 gallon pails of water.
After someone forgot to close the cover one night, I had to add about 10 bucketfulls of water. But usually it was only a couple per month or so. Depends a lot on how often the cover is up.
Brewman