Dont worry re opening. They open in thick snow conditions in other parts of the world.
Brood minimum means some varroa there.. they multiply VERY fast so better NO brood.
A towel over the frames not being inspected will keep some warmth in, but bees will cope.
Re not liking the uncapping, shower hosing, cleaning method - 2 days in the freezer, bring the frame back up to sensible temp then replace in the hive before treatment may be more acceptable to some people.. just remember that frame must be back to room temp though.