I moved some indoor over-winter plants outside 4-6 weeks ago, which of course triggered frosts and snow. This was my hasty response.
Cut two lengths of garden fence / rabbit fence
tie together to be double-wide
bend into a tunnel, propped with cinder blocks at the ends
throw two thicknesses of 2 mil plastic over it all, weigh down edges tightly
I set the plants on top of cardboard for a little insulation and to discourage slugs