You can put a small tack on the top of the door and hang a piece of fishing line down from that to attach the wreath to. Make sure the tack does not stick up high enough to hit the top jamb of the doo ... read more
I would recommend not less than 40 degrees. If the shingles are a dark color in direct sunlight they will seal in one day from the solar radiance from the sun even if temps are low.