I thought about the new dry top getting wet, but if there is a wind I want to ptotect myself as best as I could. I have used this method when I’ve needed to change in cold weather and it works for me.
Coming back to the problems a second time I would make sure the wind breaker is waterproof. Then instead of putting a wet coat in the garbage bag, I would put it back on over the wind breaker. Most modern coats will continue to provide insulation even when wet.
Zipper Eaze is a soft bees wax in tube stick. Applied to any zipper it eliminates resistance so they work easily and they don’t jam.