I've used mine about 5 times now including this morning, and they've always been okay, although my commute is only 2 miles. One really cold day I was impressed with how warm they were.
I have them in large, but maybe should have bought a bigger pair, as they are quite tight.
I open them fully, place them over my toes and pull both sides back. I then turn the bottom side around the heel, with a bit underneath, then pull the other side over and join the velcro. Be careful to line it up properly so it's about the same length at the top. I then fasten the footstrap and I'm good to go.
The bottom of the sole is quite open, so over a period of time water could seep in. It helps that I have quite a substantial rubber sole on my shoes.