If you are thinking of using the Styrofoam peanuts, (we call this ghost poo) then yes, that could help if you can place the pots into a large box, fill in around the sides with the packing peanuts but let the tops of the plants be sticking out into the sunlight. It is very important the the pots continue to drain well - and don't let them sit in their drainage water. Congratulations on using your greenhouse and overwintering your herbs - it can be a bit tricky figuring out how to keep things in a unheated greenhouse alive but what a beautiful challenge when spring arrives and your favs are ready to spend another year in your garden. Keep growing, Marianne Binetti