Hi chelty, welcome to winter sowing! I ws'd for the first time last year and loved it. Because of our variable warm/cold/warm weather last year, I put off my sowing and didn't start until mid-January with my perennials and late March with the last annuals.
I went overboard and sowed 198 containers. Out of those, only about 18 didn't germinate (it may be fewer - after a while I was too bust planting out to keep records on germination).
I used milk jugs, 2-liter bottles, and cups in plastic boxes. My favorites ended up being the 2-liters, for ease of handling, and ease in planting out.
I kept my containers in an area that got morning sun, afternoon shade.
Hope this helps. If you have questions, ask away! The folks on this forum are the best and friendliest on the site!
Pam

Chelty, I hear you on the weather changes. You never know from day to day. I had great success last year with wintersowing, though - not more than 4-5 containers that didn't work out. I lost all count of the number I planted but probably around 150. Like Pam, I kept my containers out of direct afternoon sun. I have a deck that gets dappled shade all day. That seemed to work very well.

The only problems I had (and they were not deal breakers) were the late freeze we had last year and trying to keep containers moist once they sprouted and were uncovered. That is probably as much on account of my work schedule as zone since I'm away from home for at least 10 hours a day. I hope the freeze was just a freak thing. Even so, I only lost some very tender annuals that I did not cover. Quite a lot of plants had already been planted out by then (early April) and they weathered the freeze just fine!

Pam and Linda,
Thank you so much for sharing your experiences. It gives me some confidence to jump in and give it a try. It is the best way to find out what works and what doesn't.

Thanks a bunch for taking time to reply.